Answer:
14776336
Step-by-step explanation:
Suppose that your PIN has 4 slots. Now there are 26 (upper-cased letters) + 26 (lower-cased letters) + 10 (digits) = 62 options for the 1st slots, 62 options for the 2nd slots, and so on. Therefore the total number of possible combination of PIN for all 4 slots are
[tex]62^4 = 14776336[/tex]