Well, you've sussed out the distribution of students so thats a good start. Perhaps the easier start would be to list what your random variables are and their respective probabilities:

X P(X)

25 25/148

33 33/148

40 25/148

50 50/148

Y P(Y)

25 1/4

33 1/4

40 1/4

50 1/4

Do you see why?

From here it is elementary to answer parts i and ii.