A store is selling quarts of apple juice for
$2.80 and quarts of grape juice for $2.20. In
a week the store sold 15 quarts of the juice
and received $39 from those sales. How
many quarts of apple juice (a) and quarts
of grape juice (g) did the store sell?
a + g = 15
2.8a + 2.2g = 39
[?] apple juice [ ] grape juice
=