Guess and Check #3

Three parts!

(a) I'm thinking of a number. If you multiply it by 3, then subtract 5 and finally add 10, you get 20. What number am I thinking of?
(b) I'm thinking of a number. If you multiply its square by 3 and then add 9, you get 117. What is that number?
(c) I'm thinking of a number. If you subtract 4 from the number, then multiply the result by 3 and then add 5, you get 26. What is that number?

There are many approaches to these problems - one is to guess at what the answer might be, and then adjust it to come closer to meeting the conditions in the problem. Be sure to explain the work you did to arrive at your answers!