If N sweaters can be made from x balls of wool, and the function N(x) = 20x - (10x + n) models the number of sweaters produced where n is a constant. If 500 balls of wool were used to produce 4000 sweaters, what is the value of n?


1)500

2) 1,000

3) 4,000

4) 5,000

15) 10,000