Could you help me check if following are correct answer?

a)17576

b)17576

c)11881376

d)17576

(8 points) How many strings of five uppercase English letters are there (a) that start and end with an X, if letters can be repeated? (b) that start and end with the letters BO (in that order), if letters can be repeated? (c) if letters can be repeated? (d) that start with the letters BO (in that order), if letters can be repeated