Multiplication would be first
2+4=4+2 is an example of commutative property of addition
Each of the first 3 letters can be chosen from the 23 letters, {A, B, C, …, U, V, W}, so there are 23³ possible choices.
The first 2 digits can be any number from {0, 1, 2, …, 9}, so there are 10² choices.
The last digit cannot be 0 or 9, so you can select from {1, 2, 3, …, 8} which gives 8 choices.
Then the total number of PINs that you can make is
23³ × 10² × 8 = 9,733,600
An hour and 15 minutes. Since Joe is driving 20 miles per 1/2 hour that means he is driving 40 miles every hour. We still have 10 miles left and since 20 divided by 2 is ten you would simply cut the time it takes him to drive 20 miles in half making 15 minutes. Then you add the time it takes to drive 40 miles and 10 miles and that's how you get an hour and 15 minutes. Hope this made sense!
The answer to your question is b -1