5. 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 y) y=2*x+1 else 6. Write a brief analysis of the following semantics techniques: Attribute Grammars, operational semantics, denotational semantics