please solve the problem. Thank you.

6. (a) For every number k0, let fk be the constant function fk(x)= k. Show that for every k,fk is computable. (b) Let us call an S program a straightline program if it contains no (labeled or unlabeled) instruction of the form IF V=0 GOTO L. Show by i1 duction on the length of programs that if the length of a straightline program P is k, then P(1)(x)k for all x. (c) Show that, if P is a straightline program that computes fk, then the length of P is at least k. (d) Show that no straightline S program computes the function f(x)=x+1. Conclude that the class of functions computable by straightline S programs is contained in but is not equal to the class of computable functions