Question

(purple smooth = 75, white smooth = 28, purple wrinkled = 24, white wrinkled = 8)

Account for the difference between the expected and experimental values.

Answer 1

this looks like it belongs in biology.
The proportions here are 56% purple smooth, 21% white smooth, 18% purple wrinkled, and 5% white wrinkled.
If you look at the two traits by themselves, you see that they both fit the 75-25 distribution for standard genes. The next step of analysis to see if they are linked genes is to set up a 4x4 inheritance square.