Acity distributes vehicle identification stickers using a combination of letters followed by a combination of digits, each of which may be used more than once. determine the number of possible stickers under the given circumstances. a) using 55 letters and 33 digits, how many stickers are possible

First we have to answer some elementary question before answering. 
How many digits numbers are there: 10 of course, they are 0, 1, ..., 9.
How many letters in the english alphabet: 26. 
Each time we need a character, we have 26 possibilities (since repetitions are allowed)
the stickers contains 55 letters, so the number of possible combination of the 55 letters is: 
Same thing for the 33 digits: each time 10 possibilities, resulting in 
In order to get the whole number of possibilities, simply multiply the two previous found numbers like this: