of assignment statements and their postconditiols a. a-2*b+1: 2 COmpute the we b-a-3 b so tb> 5 Le 25. Compute the weakest precondition for each of the following selection constructs and their postconditions: a. if (a b) b-2a+i else b=2*a; b > 1 b. if (x y) else (x3) 26. Explain the four criteria for proving the correctness of a logical pretest loop construct of the form while B do S and. 27. Prove that (n+1).n1. 28. Prove the following program is correct of assignment statements and their postconditiols a. a-2*b+1: 2 COmpute the we b-a-3 b so tb> 5 Le 25. Compute the weakest precondition for each of the following selection constructs and their postconditions: a. if (a b) b-2a+i else b=2*a; b > 1 b. if (x y) else (x3) 26. Explain the four criteria for proving the correctness of a logical pretest loop construct of the form while B do S and. 27. Prove that (n+1).n1. 28. Prove the following program is correct