Subtraction method return NaN result

Question

l am trying to subtract two numbers which already exists. when I click on cut method, its returning NaN

export class Tab2Page implements OnInit {
  categories: AngularFireList<any>;
  userBlnc :any // user balance in database 

  constructor(public af: AngularFireDatabase, public afAuth: AngularFireAuth, public router: Router,
public a: LoadingController, public m: AlertController) { }


  ngOnInit(): void {
    this.afAuth.authState.subscribe(async user => {
      if (user) {
        // Getting user balance from database 
        this.af.list("/users/" + user.uid + '/profile').valueChanges().subscribe((data: any) => {
          this.userBlnc = data; // output array
        })
      } else {
        this.router.navigate(['signin'])
      }

    })
  }

 // alert dialog to confirm Subtraction
  async open(a) {
    const alert = await this.m.create({
      cssClass: 'my-custom-class',
      message: "شراء فئة" + a.name + " بسعر " + a.price + " د٫ع ",
      buttons: [
        {
          text: 'الغاء',
          role: 'cancel',
          handler: () => {
            console.log('Confirm Cancel');
          }
        }, {
          text: 'شراء',
          cssClass: 'btn_buy',
          handler: () => {
            this.cut(a);
          }
        }
      ]
    });

    await alert.present();
  }

 // excite  Subtraction
  async cut(a) {

    let fpaValue: any
    if (Number(this.userBlnc[0])) {
      if ( Number(a.price)>Number(this.userBlnc[0])) {
        fpaValue = (Number(a.price) - Number(this.userBlnc[0]))
        console.log(fpaValue)
        alert(fpaValue)
      } else {
        alert('no balance engough')
      }
    }

  }

}

Answer 1

I found the issue. I realized the numbers in my database were written in " Arabic font " So thats why he return NaN result . So l changed to English numbers and he is working fine . :)