At Oxnard University, a student ID consists of two letters (26 possibilities) followed by four digits (10

Question:

At Oxnard University, a student ID consists of two letters (26 possibilities) followed by four digits (10 possibilities).
(a) How many unique student IDs can be created?
(b) Would one letter followed by three digits suffice for a university with 40,000 students?
(c) Why is extra capacity in student IDs a good idea?