I need to move my operations to another file

I am something new in Java and I have a program that displays a graphical interface and calculates the roots of a second degree equation (x1 and x2), if the discriminant is < 0 and several other cases:

import javax.swing.JFrame;
import javax.swing.JTextField;
import javax.swing.JButton;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextArea;
import javax.swing.JScrollPane;
import java.awt.GridLayout;
import java.awt.FlowLayout;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;

public class CuadraticasGUI extends JFrame implements ActionListener

{

    private JTextField tfA, tfB, tfC;
    private JButton bCalcular, bSalir;
    private JTextArea taDatos, taDatos2;
    private JPanel panel1, panel2;

    private CalculosEC calculos = new CalculosEC();

        public CuadraticasGUI()
        {
            super("Calculo de las raices de una ecuacion cuadratica de 2do grado." );
            tfA      = new JTextField();
            tfB      = new JTextField();
            tfC      = new JTextField();
            bCalcular= new JButton("Calcular Raices");
            bSalir   = new JButton("Salir");
            panel1   = new JPanel();
            panel2   = new JPanel();            
            taDatos  = new JTextArea(10,30);

            bSalir.addActionListener(this);
            bCalcular.addActionListener(this);

            panel1.setLayout(new GridLayout(4,2));
            panel2.setLayout(new FlowLayout());
            panel1.add(new JLabel("Coeficiente A = "));
            panel1.add(tfA);
            panel1.add(new JLabel("Coeficiente B = "));
            panel1.add(tfB);
            panel1.add(new JLabel("Coeficiente C = "));
            panel1.add(tfC);
            panel1.add(bCalcular);
            panel1.add(bSalir);
            panel2.add(panel1);
            panel2.add(new JScrollPane(taDatos));
            add(panel2);
            setSize(500,350);
            setVisible(true);
        }

        public void actionPerformed(ActionEvent event)
        {
            if(event.getSource()== bSalir)

            {
                System.exit(0);

            }
            if(event.getSource()== bCalcular)
            {
                String strA=tfA.getText();
                float a=Float.parseFloat(strA);
                String strB=tfB.getText();
                float b=Float.parseFloat(strB);

                String strC=tfC.getText();
                float c=Float.parseFloat(strC);

                float disc = calculos.CuadraticasGUI(a, b, c);


                if(a==0)
                {
                    if(b==0)
                    {
                     taDatos.setText("La ecuacion no existe");
                    }
                    else
                    {
                        float x=(-c)/(b);
                        taDatos.setText("A es igual a 0 por lo tanto X="+x);
                    }


                }
                else{

                    double x1,x2=0;
                    if(disc>0)
                    {
                      x1=(-b+Math.sqrt(disc))/(2*a);
                      x2=(-b-Math.sqrt(disc))/(2*a);
                      taDatos.setText("X1= " +x1+ " X2= " +x2);

                    }
                    if(disc==0)
                    {
                    double  x=(-b)/(2*a);
                        taDatos.setText("X= "+x);
                    }
                    if(disc<0)
                    {
                        taDatos.setText("Las raices son imaginarias");
                    }
                }

            }
        }





        public static void main(String args[])
        {
            CuadraticasGUI cuadratica = new CuadraticasGUI();
        }
}

So, what I want to do and I can not do is move operations to another file

Code:

public class CalculosEC
{
    public float CuadraticasGUI(float a, float b, float c)
    {

        float disc=0;
        disc=b*b-4*a*c;     
        return disc;

    }
}

As you can see there, I only calculate disc. and I use the return so that in CuadraticasGUI it passes through the if and display depending on the conditions.

The program works perfectly as it happens, but I want to pass all the operations from if (a == 0) to the other file (CalculosEC) and in CuadraticasGUI to deploy, depending on the situation, the results.

Would someone be so kind to help me?