During the summer months Terry makes and sells necklaces on the beach. Last summer he sold the necklaces for $$ 10$ each and his sales averaged 20 per day. When he increased the price by
S1, he found that the average decreased by two sales per day.
(a) Find the demand function, assuming that it is linear.
(b) If the material for each necklace costs Terry $$ 6,$ what should the selling price be to maximize his profit?