Creating Calculator- Troubles because + is doing this (7+3 = 73) instead of (7+3=10)

I've looked around a lot and all I've found is that I'm supposed to concatenate the string becuase JS is reading the + sign as just putting them together. Not adding.


function formula()
{
var costa = calculator.costa.value;
var profita = calculator.profita.value;
var yeilda = calculator.yeilda.value;
var answer = Math.abs((costa + profita) / yeilda);
calculator.ans.value = answer;
return false;
}

The variable I'm having the trouble with is ANSWER. costa and profita are supposed to be added together, not just put next to each other.

Here is the calculator: http://qualitygrainservices.com/calc.php

I hope I gave enough information for everyone to sorta know what I'm having trouble with. If not please say something so I can give you more!

Form values are always returned as strings,
convert them to number format before math operations with
parseFloat(value) or Number(value)

Form values are always returned as strings,
convert them to number format before math operations with
parseFloat(value) or Number(value)

Whoa. I have no idea what you said. I'm sorry! I just started all of this today...

Nevermind. I figured it out. I still have no idea what you were talking about though. Lol.