A clever sports economics student asked the Athletic Director at his or her university to dig back into the records for data on attendance and prices at the college's baseball games. The student's research revealed the following attendance demand function for alumni and other boosters:
PB = $24 - (1/20) AB.
PB = booster price and AB = booster attendance.
Draw the marginal revenue function. At what level of attendance is marginal revenue equal to zero? At what price?