For the first four letters in the English alphabet, a. List the possible permutations of three letters

Question:

For the first four letters in the English alphabet,
a. List the possible permutations of three letters from the four.
b. List the possible combinations of three letters from the four.
c. Use parts (a) and (b) to obtain 4P3 and 4C3.
d. Use the permutations and combinations rules to obtain 4P3 and 4C3. Compare your answers in parts (c) and (d).