Question 1134573
a. With repetition = 26*26*26*10*10*10*10 = 175,760,000
b. No repetition with letters (available letters decreases by 1 each time) = 26*25*24*10*10*10*10 = 156,000,000
c. No repetition with digits (available digits decrease by 1 each time) = 26*26*26*10*9*8*7 = 88,583,040