B, d. Please explain with general formulas that are then applied to the problem.

Counting Tuples 15. For each of the following cases, find the number of strings over the alphabet a, b, c, d, e that satisfy the given conditions a. Length 4, begins with a or b, contains at least one c. b. Length 5, begins with a, ends with b, contains at least one c or d. c. Length 6, begins with d, ends with b or d, contains no c's. d. Length 6, contains at least one a and at least one b