We will take x, the spacing between the "spots" on the wall, as our observable.
How does x depend on
d, the distance between the "atoms" on the slide?
L, the distance to the wall?
λ, the wavelength of light ("color")?
For each combination below of x, d, L, and λ, identify which two variables are constant and whether the remaining two variables are directly or inversely related.
If the slide is moved closer to the screen, what will happen to the diffraction pattern?
If the spacing between features on the slide is reduced, does the diffraction pattern get larger or smaller?
For a given array on the slide, will red or green light give a larger diffraction pattern? Also look through the slide at a point source of white light (such as a miniMaglite with the lens removed). Each spot breaks into the full visible spectrum. Which color is diffracted the most? Which color is diffracted the least?
Combine your four variables into one equation. Since x/L = tanΦ = sinΦ/cosΦ and cosΦ ≈ 1 for small angles, do you get the Fraunhofer equation?