Please help and show work ​

You are designing a rectangular pet pen for your new baby puppy. you have 30 feet of fencing you would like the fencing to be 6 1/3 feet longer than the width

6x + 3y = -6 2x + y = -2 a. x = 0, y = -2 b. infinite solutions c. x = -1, y = 0 d. no solution

1) prove that 731^3−631^3 is divisible by 100 2) prove that 99^3−74^3 is divisible by 25