PLEASE HELP!!
After losing 3 baseball cards, Peter gave half of his remaining cards to Bobby. If Peter gave Bobby 9 baseball cards, how many cards did Peter start with?

Linear equation:  1 /2 (x - 3) = 9

Bobby claims that Peter started with 21 cards. Which statements are true about verifying Bobby’s claim? Check all that apply.

1. Substitute 21 for x in the original equation.
2. Substitute any number for x in the original equation.
3. Bobby’s claim that x = 21 is correct.
4. The result of verifying Bobby’s work is 9 = 9.
5. The result of verifying Bobby’s work is 21 = 21.