i need help with questions (c) and (d)

here is a definition of letter substitution

7) Prove that the regular languages are closed under each of the following operations: a) pref(L) = {w: 2x e ** (wx L)). b) suff(L) = {w: 3x S* (XW L)). c) reverse(L) = (x e E*:x-wR for some wel). d) letter substitution (as defined in Section 8.3). The regular languages are closed under letter substitution, defined as follows: consider any two alphabets, 2, and 22. Let sub be any function from 2 to 2*. Then letsub is a letter substitution function from Lito L, iff letsub(LI) {w e * : 3y e L. (w=y except that every character cofy has been replaced by sub(c))}. For example, suppose that 21 = {a,b), 22 = {0,1), sub(a)=0, and sub(b) 1. Then letsub {a'b":n20})= {0"12:20). We leave the proof that the regular languages are closed under letter substitution as an exercise