Answer:
9x - 9y + 8
Step-by-step explanation:
Simplify means to solve, but in this context it means to "shorten" it by adding the like terms together:
7x - 9y + 15 + 2x - 7
rearrange to make it easier, optional
7x + 2x - 9y + 15 - 7
add like terms
9x - 9y + 8
