Answer:
-7/45
Explanation:
First, find the lowest common denominator for 9 and 15. It's 45. Make both fractions over 45 by multiplying the top and bottom by the same number.

Since 15*3=45, multiply the top by 3 also. Since 9*5=45, multiply the top by 5 also.

Combine the fractions
Answer in lowest terms