You need to learn how to figure it out on your own, giving you the answers wont help you further on, when it is only going to get harder.
1) Write a basic formula, I'll give you a hint: x * ? = 5.00
Figure out what ? is, move it over to the other side, and you'll know what X is (the original price).
2) (10.26 - 9.50) / ? = x * 100 (to get a whole number in percentage terms)
Rest are the same principle, figure out a basic formula, but I don't got time to do the rest.