Add arrays of a MySQL query in PHP -

Make a query to my database which gives me the following results:

[400,600]

  

Note: this query is done with mysqli where obviously in array it is called from a loop while in this way $columna_gastos['costo_gastos']

Then I need the response values of that array can be added together and the result is as follows:

1000

This is the calculation code:

    while($columna_gastos = $resultado_del_query_gasto->fetch_assoc()){
     if(true){
        $total_gasto[$contador_get_values_gastos][0] = $datos_de_viaje_cond_clie[$contador_get_values_gastos][0];
        $total_gasto[$contador_get_values_gastos][1] = $total_gasto[$contador_get_values_gastos] + $columnas_de_gastos['PRECIO_GASTO'];

        $contador_get_values_gastos = $contador_get_values_gastos + 1;  
      }

  }

  

The error is in this line of code: $total_gasto[$contador_get_values_gastos][1] = $total_gasto[$contador_get_values_gastos] + $columnas_de_gastos['PRECIO_GASTO'];