25. compute the weakest precondition for each of the following selection constructs and their postconditions: a. if (a == b) b = 2 * a + 1 else b = 2 * a; {b > 1} b. if (x < y) x = x + 1 else x = 3 * x {x < 0} c. if (x > y) y = 2 * x + 1 else y = 3 * x - 1; {y > 3}