May I ask Vuejs how to get the binding value after calculation?

< div id= "app" >

<input v-model="c.a">
<input v-model="c.b">
<input :value="c.a*c.b">

< / div >

var vm = new Vue ({

el:"-sharpapp",
data:{
    c:{}
},
...

});

because the official document says that the form with v-model ignores the value attribute, how should I implement it if I want to get the values of three input boxes and submit them to the background as the same object c (it can be obtained directly in angularjs, is there a similar way to MVVM"s Vuejs)?
has tried to bind to the third box in data and set the calculation rules (multiplication), but it seems that Vue does not recognize
< input vMube model = "c.d" >
.
data: {

c:{
   //d:this.c.a*this.c.b
}

},
.
ask for advice!

Sep.01,2021

Compute properties learn about
https://cn.vuejs.org/v2/api/?.

you can easily implement
example

with computed .
<template>
  <div id="app">
    <input v-model="c.a">
    <input v-model="c.b">
    <input :value="v">
    {{ c }}
  </div>
</template>
<script>
  export default {
    data() {
      return {
        c: {a: 0, b: 0, c: 0},
      };
    },
    computed: {
      v() {
        const v = this.c.a * this.c.b;
        this.c.c = v;
        return v;
      },
    },
  };
</script>
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