I have been trying to figure this out all day. please help. If the cost of one unit is $10, 20 units will be sold. If the cost is $11, 18 units will be sold. a) Find the demand function assuming it is linear. b) If the materials for each unit cost $6 what should the selling price be to maximise profit? I believe that the demand function is p(x)=-.5x+20 but I cannot figure out how to maximise profit. PLEASE HELP!