Find mangle1 and mangle2. justify your answer

Pls , the question is in the picture!

Which of these people has balanced their checkbook correctly? oa. gary: the balance in his check register is $500 and the balance in his bank statement is $500. b. gail: the balance in her check register is $400 and the balance in her bank statement is $500. c. gavin: the balance in his check register is $500 and the balance in his bank statement is $510.

How can you decide witch operations to use to slice a two step equation