ABC bookstore sells new books, n, for $15 and used books, u, for $7. The store earned $234 in revenue last month. The store sold 2 more used books than new books. Which system of equations represents this scenario?
A) 7n+ 15u= 234; u= n+ 2
B) 7n+ 15u= 234; u= n- 2
C) 15n + 7u= 234; u= n- 2
D) 15n + 7u= 234; u= n+ 2