Assume there is unlimited supply of M&M's and of bubblegum, which cost one cent each, and of sourballs, peppermints, and gumdrops, which cost two cents each. You're going to buy n cents' worth of candy, one piece at a time. Let an be number of selection sequences that end up costing n cents. Thus a sub 2 = 7(mm, mb, bb, bm, s, p, g). Notice that in this problem order of choosing matters.
Part (a) Find a recursion relation of a sub n.
Part (b) Solve the recursion, and give a formula for a sub n.