3/3+15/15

2

Reason: 3/3 = 1 and 15/15 = 1, so 1 + 1 = 2. (You can also see it by common-denominator: 3/3 = 45/45 and 15/15 = 45/45, then 45/45 + 45/45 = 90/45 = 2.)