A confirmation code consists of five letters followed by two digits, all of which can be repeated. Which of these is/are appropriate counting techniques to figure out how many confirmation numbers are...

A confirmation code consists of five letters followed by two digits, all of which can be repeated. Which of these is/are appropriate counting techniques to figure out how many confirmation numbers are possible?

i)   Fundamental Counting Principle

ii)  Permutations

iii) Combinations

Choose the best answer below and explain:

None of these?

1 and 2 only?

2 and three only?

1 and 3 only?