a) Since you need the probability of the person being a freshman and a C grade student, the probability will be 8/45 (number of C grade student who are freshmen divided by the total number of people)
b) You have to add the two probabilities that you are going to find whenever you see an 'or' function.
Student is a sophomore = 22/45
Student made an A = 7/45
Probability = 22/45 + 7/45
= 29/45
c) Whenever you see an 'and' function, you have to multiply up the probability.
Student is a sophomore = 22/45
Student made an A = 7/45
Probability = 22/45 * 7/45
= 154/2025
d) Student made a D = 5/45
Student is a freshman = 23/45
Probability = 5/45 + 23/45
= 28/45
Hopefully, this made sense.