Suppose that a and b are integers, a ≡ 4 (mod 13), and b ≡ 9 (mod 13). find the integer c with 0 ≤ c ≤ 12 such that a. c ≡ 9a (mod 13). b. c ≡ 11b (mod 13). c. c ≡ a + b (mod 13). d. c ≡ 2a + 3b (mod 13). e. c ≡ a2 + b2 (mod 13). f ) c ≡ a3 − b3 (mod 13)