1. A company sells posters at $4 each and sells an average of 1000 posters per day. A survey shows that, for each $1 increase in price per poster, 100 fewer posters would be sold per day.
   1. Write an equation to express the revenue, R(x) dollars, in terms of a price increase of "x" dollars. What price per poster gives the maximum revenue? What would be the maximum revenue How many posters would be sold when the revenue is at a maximum?