Delete item from firebase [Ionic]

I can add items to firebase, but I can not delete it. If I delete an element, I delete them all. This is my code

  <ion-list>
    <ion-item *ngFor="let item of arrData; let i = index" (click)="btnAction(i)" > 
      <h3><strong>Name: </strong>{{item.myInputName}}</h3>
      <h4><strong>Age: </strong>{{item.myInputNumber}}</h4>
    </ion-item> 
 </ion-list>

import { AngularFireDatabase } from 'angularfire2/database';
...
  arrData = [];
  $key?:string;
  myInputName: string;
  myInputNumber: number;
  usuarios:any = [];

  constructor(public navCtrl: NavController, 
                public navParams: NavParams,
                private afDB: AngularFireDatabase,
          private action: ActionSheetController) {

 this.afDB.list("myUsers").valueChanges().subscribe(_data =>{
        this.arrData = _data;

        console.log(this.arrData);
    });
  }

btnAction(usuarios){
  console.log(usuarios);
  this.action.create({
    title: '${usuarios.myInputName}',
    buttons: [
    {text: "Editar",
    handler: ()=>{
      //tenemos que pasar un parametro para editar.

    }
  },
    {text: "Borrar",
    role: "destructive",
    handler: ()=>{
      //tenemos que pasar un parametro de eliminacion.
      //this.afDB.list("myUsers").remove(usuarios.$key);
      console.log(this.arrData[usuarios]);
      //this.afDB.list("/myUsers/").remove(this.arrData[usuarios].$key);
      this.afDB.list('/myUsers/${ this.arrData[usuarios]}').remove();

        }

....

none of the this.afDB ... It does not work. it does not eliminate the item but all of them.

Thanks in advance