Iterate Through A Table For Values Of Drop Down Menus?

I wish to get the values for the 3rd and 4th cell of each row where these contain drop down menus. I've tried various ways but my code doesn't seem to iterate through rows of a table. I can get the values for the first row, but not the rest. There's isn't a fixed row size for the table as the user will be able to add and delete them.

I've put the values in separate arrays but instead of the array containing say [10, 20] it contains [10, 10] as it just duplicates the first row's values.

Here's my code that I have so far:

function calculate(){
var len = document.getElementById(arguments[1]).rows.length;
var cMenus = [];
var gMenus= [];

[Code]...

I've tried adding j to the arguments or putting it in "[]" but nothing seems to work. I don't think the platform I'm using supports jquery,