Explain why a + b = b + a

Based upon past experience, barry expects no overdrafts. he expects no 2nd copies of statements. barry estimates that he will use network atms about 5 times a month with either bank. barry decides in the end to choose eecu. assuming that both banks provide the necessary services equally well, and based upon the tables of fees given above, how much can barry reasonably expect to save annually by choosing eecu in this case over e-town bank? a. $72 b. $78 c. $144 d. $24

[10 points, algebra 2-simplifying complex fractions]according to my answer key the restrictions are -1 and 4. but why not positive 1?

What is the answer to this question? i'm a bit stumped. also how do i do it? 5(x - 4) = 2(x + 5)