How to find intensity in double slit

[kelambumlm]

1. Homework Statement
the two slit of a double slit each have a width of 0.140mm and a distance between centers of 0.840mm. what the approximate intensity of orders m=o to m=6?

2. Homework Equations
i want to use the I/Io = (E/Eo)^2 but some book use
I = 4Ao^2sin^2 beta/beta^2cos^2gamma. i also don't know how to find the value for beta and gamma.

anybody please help me...

3. The Attempt at a Solution

 

[Chi Meson]

I'm sorry, I even went to my old 3rd Year Optics textbook, and I cannot find the method for answering this problem. Try reposting this in the "Advanced" forum.