By using jslint repeatedly and researching to understand the errors, I've come to the following:

HTML Code:
```var document,
runtime = document.getElementById('runtime'),
resultPitStops = document.getElementById('resultPitStops');

function formFuel(form) {
var a = form.elements.tank.value,
b = form.elements.driveMinutes.value,
c = form.elements.driveSeconds.value,
d = form.elements.consumed.value,
used = a - d, // get the amount of fuel used  -->
secs = b * 60, // convert minutes into seconds  -->
secstotal = secs + c, // add minutes and seconds to get total seconds  -->
secsPerCC = secstotal / used, // divide the number of seconds into the used fuel amount for secs per cc  -->
seconds = secsPerCC % 60, // use modulus operator to get the remainder and convert into seconds figure  -->
minutes = math.floor(secsPerCC / 60),  // get the minute figure as a digit  -->
runtime2 = minutes + ":" + seconds; // concatenate everything into minutes and seconds  -->

form.elements.ans.value = runtime2;
}

function heatpit(form) {
var e = form.elements.LENGTH.value, // put LENGTH field value into variable e  -->
f = form.elements.STOPS.value, // put STOPS field value into variable f  -->
secs2 = e * 60, // convert the minutes into seconds  -->
periods = f + '1', // add 1 to the pit stop number get the total  number of divisions throughout the period  -->
result2 = secs2 / periods, // divide the full time by the number of periods  -->
seconds = result2 % 60, // use modulus operator to get the remainder and convert into seconds figure  -->
minutes = math.floor(result2 / 60), // get the minute figure as a digit  -->
time = minutes + ":" + seconds; // concatenate everything into minutes and seconds  -->

form.elements.between.value = time; // display in the "between" field s/b "time" value  -->
}

runtime.onclick = function () { // https://developer.mozilla.org/en/DOM/element.onclick
var form = document.getElementById('form1');
formFuel(form);
}

resultPitStops.onclick = function () {
var form = document.getElementById('form2');
heatpit(form);
}```
I still don't understand why a semi-colon is a problem inside the last two functions. When I remove them, then more errors appear. I also don't know how to 'define' math.

This has been a good learning experience.