Please help with calculation

[edp1959]

I'm very new with javascript so I need help with what I think should be a very simple calculation. Here's what I'm trying to do:

Webpage contents:
drop down menu (S2) with set values for each item
drop down menu (S3) with set values for each item
form field (T1) for user input of number
push button (B3) to perform calculation
form field (T5) for calculation result

When the user selects items from S2 and S3 and puts a number in T1 then clicks B3 the result should show in T5.

This does not work correctly, the problem seems to be when I try to add 6 to y, because it gives me the correct answer with just y.

function ratings()
{
var t=document.cMount.S2.value;
var y=document.cMount.T1.value;
if (document.cMount.S3.value==12){
var Lmax=((2*t)*(146700/3))/y;}

if (document.cMount.S3.value==25){
var Lmax=((2*t)*(146700/3))/(y+6);}

if (document.cMount.S3.value==64){
var Lmax=((2*t)*(146700/3))/(y+6);}

document.cMount.T5.value=Lmax.toFixed(0);

[jntcomputers]

So, what you're saying is you get the same answer as the first if statement where s3 == 12? Could be a problem with the form and not the calculations?

[edp1959]

This gives me a correct value in T5, i.e. 2156
if (document.cMount.S3.value==12){
var Lmax=((2*t)*(146700/3))/y;}


The value these two give in T5 is NaN
if (document.cMount.S3.value==25){
var Lmax=((2*t)*(146700/3))/(y+6);}

if (document.cMount.S3.value==64){
var Lmax=((2*t)*(146700/3))/(y+6);}

[edp1959]

I'm sorry I told you wrong, this is what I am getting.

Here are the values that this example is based on:
S2: 2.646
T1: 120

This gives me a correct value in T5, i.e. 2156
if (document.cMount.S3.value==12){
var Lmax=((2*t)*(146700/3))/y;}

Using the same values as above these two give me (2156 +6) 2162. The correct answer should be 2054.
if (document.cMount.S3.value==25){
var Lmax=((2*t)*(146700/3))/(y+6);}

if (document.cMount.S3.value==64){
var Lmax=((2*t)*(146700/3))/(y+6);}

[jntcomputers]

Try creating a third variable like

x = y + 6;

then

var Lmax=((2*t)*(146700/3))/x;

OR

try this

var Lmax=(((2*t)*(146700/3))/(y+6));}

(adding parenthesis around the whle equation...

[edp1959]

var z=y+6

var Lmax=((2*t)*(146700/3))/z;

This gives me T5 = NaN