When Katutura Power & Money, Inc. charges N$600 for a seminar on management techniques, it attracts 1000 people. For each N$20 decrease in the charge, an additional 100 people will attend the seminar. However, due to limited facilities, no more than 2500 can be accommodated.

(a) Find an expression for the total revenue, if there are x N$20 decreases in the price

(b) Find the value of x that leads to maximum revenue, the amount of maximum revenue, and the number of people attending in this case.