If all is allowed that means repetition is allowed including 0. If so:
You start with 2 letters out of the 26 letters of the alphabet
For the letters you have 26 choice for the first letter and 26 for the second, that make 26 x 26 = 676
For the digit, you have the choice among 10 digits:
for the first digit you have 10 choices,
for the 2nd digit you have 10 choices
for the 3rd digit you have 10 choices
for the 4th digit you have 10 choices
for the 5th digit you have 10 choices
Total choices for the digits is 10x10x10x10x10 = 100,000
Total combination (2 letters and 5 digits) = 676 x 100,000 = 67,000,000 ways
