We know that 9 cows + 6 cows add up to 15 cows,
and 9 trees + 6 trees add up to 15 trees,
and 9 cars + 6 cars add up to 15 cars,
so we're pretty sure that
9 twelfths + 6 twelfths add up to 15 twelfths.
9/12 + 6/12 = 15/12
It wants us to simplify the answer, so
we can divide top and bottom by 3 :
15/12 = 5/4 = 1 and 1/4 .
