In order to calculate the number of different plates, let's check the number of possible values for each digit or letter in the plate.
Each letter has 26 possible values (from A to Z) and each digit has 10 possible values (from 0 to 9).
Since we have two letters and two digits in this order, the total number of different plates is:
The number of different plates is 67,600, therefore the correct option is the third one.