20. Given b-(c+ 10)/3 and post condition Ib > 6) elve the precondition in terms of y, 4 pts) 21. Elminate direct left recursion using the rules below and give the new grammar rules without direct left recursion for the below grammar rules. (6 pts For A A+BIB 18 For each nonterminal, A, L.) Group the A rules as A >Ao, .1Aam 1 p1 1 B2 1 Bn where none of the p's bepins with A 2.1 Replace the original A-rules with A ? M 1 ?2A, 1-1 w. 22 Using static scoping in nesting, what would be the value of x in sub2 if you called big()16 pts) unction big) ( function subl0 f var x-7, sub20: function sub20 var x1 subi0 (circle the correct answer) none of the above