Buying computers for your coworkers

You are given the task of buying office computers for your coworkers. There are
three brands to choose from: Apple, HP and Dell. The HP and Dell computers
cost $1,000 each and the Apple computers cost $2,000.
(a.) How many different purchases can you make if you must spend $15,000?
(b.) How many different purchases can you make if you must spend $15,000 and you must buy more HP computers than Apple computers?