Both these questions use the law of products.
The main idea is that if you want to count something that can be split into independent choices, then the total is the product of the number of possibilities for each independent choice.
For example, an outfit consists of a hat, a shirt, and pants. You have 3 hats, 4 shirts, and 2 pants. How many possible outfits are there? 3 x 4 x 2 = 24
So for each problem, first split it up into independent choices that have to be made. Try to work each problem a bit further in this direction.
Hint for 1a, the independent choices are what to pick for the first letter, what to pick for the second letter, etc.