JSFiddle - React, Tailwind, and code Playground

HTML

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<title>Cost Savings Calculator</title>



<script language="JavaScript">


<!-- Begin CE MP Savings Calc script
function  doMath3() {
    var one = parseInt(document.theForm3.elements[0].value);
    var two = parseInt(document.theForm3.elements[1].value);
    var selection = document.getElementsByName("zone")[0].value;

    if(selection == "z4"){
        var prodZ4 = (((one  *   two) * 4.25) *12) - 1680;
        alert("Your yearly savings if you buy a Commuter Express Zone 4 monthly pass is $"  +  prodZ4  +  ".");
    }
    else if(selection == "z3"){
        var prodZ3 = (((one  *   two) * 3.75) *12) - 1488;
        alert("Your yearly savings if you buy a Commuter Express Zone 3 monthly pass is $"  +  prodZ3  +  ".");
    }
    else if(selection == "z2"){
        var prodZ2 = (((one  *   two) * 3) *12) - 1200;
        alert("Your yearly savings if you buy a Commuter Express Zone 2 monthly pass is $"  +  prodZ2  +  ".");
    }
    else if(selection == "z1"){
        var prodZ1 = (((one  *   two) * 2.5) *12) - 960;
        alert("Your yearly savings if you buy a Commuter Express Zone 1 monthly pass is $"  +  prodZ1  +  ".");
    }
    else if(selection == "Base"){
        var prodBase = (((one  *   two) * 1.5) *12) - 684;
        alert("Your yearly savings if you buy a Commuter Express Base monthly pass is $"  +  prodBase  +  ".");
    }
}

// End CE MP Savings Calc script -->


</script>



</head>

<body>

<form name="theForm3">
Days you commute monthly:
<input type="text">
Daily trips on Commuter Express:
<input type="text">
Choose Zone: <select name="zone">
<option value="Base">Base</option>
<option value="z1">Zone 1</option>
<option value="z2">Zone 2</option>
<option value="z3">Zone 3</option>
<option value="z4">Zone...