JSFiddle - React, Tailwind, and code Playground

HTML

<input name="name1" id="id1" value="" type="radio" >&nbsp;&nbsp;Amount 1&nbsp;$ <input name="amtname" size="5" maxlength="7" value="" ><br><br>
<input name="name1" id="id2" value="" type="radio" >&nbsp;&nbsp;Amount 2&nbsp;$ <input name="amtname" size="5" maxlength="7" value="" ><br>

JavaScript

function updateBoth() {
    document.getElementsByName("amtname")[0].value = this.value;
    document.getElementsByName("amtname")[1].value = this.value
}

document.getElementsByName("amtname")[0].oninput = updateBoth;
document.getElementsByName("amtname")[1].oninput = updateBoth;