4) When you get to college you will be assigned a new Student Identification Number. If this ID is 5 number digits and 2 letters long, how many possible students can the school accommodate?

The IDs are of the form LL, where D is a digit and L is a letter. There are 10 digits and 26 letters in English.
This gives you 10*10*10*10*10*26*26 possible combinations, or that many possible students who can use that system.

That’s 67,600,000 students.