Do every even question

A. Prove the following statements with contrapositive proof. (In each case, think about how a direct proof would work. In most cases contrapositive is easier.) 1. Suppose n E Z. If n is even, then n is even. 2. Suppose n E Z. If n2 is odd, then n is odd. 3. Suppose a, be Z. If a2(62 -26) is odd, then a and b are odd. 4. Suppose a, b, cE Z. If a does not divide bc, then a does not divide b. 5. Suppose x ER. If x2 +5x 0 then x> -1. 7. Suppose a, b E Z. If both ab and a + b are even, then both a and b are even. 8. Suppose x ER. If x5 - 4x4+ 3x3 -x2 +3x -420, then x 2 0. 9. Suppose n EZ. If 3In2, then 3tn. 10. Suppose x, y,z EZ and x * 0. If xyz, then xty and x z. 11. Suppose x, yEZ. If x (y + 3) is even, then x is even or y is odd. 12. Suppose a E Z. If a2 is not divisible by 4, then a is odd. 13. Suppose x ER. If x5 + 7x3 +5x2x4+x2+8, then x 20