Compute the weakest precondition for each of the following assignment statements and postconditions:

a. a = 2 * (b - 1) - 1 {a > 0}

b. b = (c + 10) / 3 {b > 6}

c. a = a + 2 * b - 1 {a > 1}

d. x = 2 * y + x - 1 {x > 11}