JSFiddle - React, Tailwind, and code Playground

HTML

<form name="myForm">
    <input type="radio" name="myRadios"  value="3" >3%</value>
    <input type="radio" name="myRadios"  value="5" >5%</value>
    <input type="radio" name="myRadios"  value="7" >7%</value>
</form>
Amount: <span id="amount"></span>

<script>
var amountField = document.getElementById('amount');
var rad = document.myForm.myRadios;
var prev = null;
for(var i = 0; i < rad.length; i++) {
    rad[i].onclick = function() {
        console.log(this.value);
        if(this !== prev) {
            prev = this;
            amountField.textContent = 1000+1000*this.value/100;
        }
    };
}
</script>