How take an input and add it

How can I ask the user for two different numbers and add them?

This is a pretty basic homework question which you should really answer using a Javascript textbook. But

First Number <input type = "text" id = "first"><br>
Second Number <input type = "text" id = "second"><br>
<input type = "button" value = "Add 'em up" onclick = "add()"><br>
Total <input type = text" id = "total" readonly>


<script type = "text/javascript">
function add() {
var a = document.getElementById("first").value;
var b = document.getElementById("second").value;
var t = Number(a) + Number (b); // convert from strings to numbers
document.getElementById("total").value = t;
}

</script>


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