Let n new books and u old books were sold last year.
Revenue from new books = 12n
Revenue from old books = 8u
Last month, the store earned $112 as revenue, so we can write:
12n + 8u = 112
The store sold 4 more used books than new books, so we can write:
u = n + 4
Using the value of u, in above equation, we get:
12n + 8(n+4) = 112
12n +8n + 32 = 112
20n= 80
⇒
n=4
Since,
u = n + 4
u = 4 + 4 = 8
Thus, the store sold 4 new books and 8 old books last month. So the correct option is A
