Compute the weakest precondition for each of the following assignment statements

and postconditions:

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

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

c. a = 2 * b + 1;

b = a - 3

{b < 0}

d. if (x > y)

y = 2 * x + 1

else

y = 3 * x - 1; {y > 3}