Getting multiple checkbox value using Angular10

app.component.html

<form #x="ngForm" (ngSubmit)="submit()">
    <div class="form-check form-check-inline">
            <input [(ngModel)]="details.a" #a="ngModel" type="checkbox" value="1">
            <label class="form-check-label" for="inlineCheckbox1">HELLO A</label>
        </div>
    <div class="form-check form-check-inline">
            <input [(ngModel)]="details.b" #b="ngModel" type="checkbox" value="2">
            <label class="form-check-label" for="inlineCheckbox1">HELLO B</label>
        </div>
    <div class="form-check form-check-inline">
            <input [(ngModel)]="details.c" #c="ngModel" type="checkbox" value="3">
            <label class="form-check-label" for="inlineCheckbox1">HELLO C</label>
        </div>

<button [disabled]="!x.valid" >Submit</button>

</form>

App.Component.ts

export class AppComponent implements OnInit {
details:{
    a:boolean,
    b:boolean,
    c:boolean
} = {
    a:null,
    b:null,
    c:null
}
constructor(){
}
submit(){
    console.log(this.details) //to get true or false if checked
 }  

I'm trying to get the status and the value of the checkbox , I need to assign the value to variable if checked

EXAMPLE:

if 1 and 3 are checked var x = 1 + 3 x = 4