Compute the weakest precondition for each of the following statements and postconditions: (1) a = 5 * (c (2) x = 3 * Y 3) + 7 (a > 12) x + 5 {x < 8} (3) a= (2 b + 3); b = 5a + 3; {b < 8} (4) if (x > y) y = 5 * x + 3; else y = 3 *x - 9; {y < 18}