Answer:
-10y
Step-by-step explanation:
(7x - y) - (7x + 9y)
This is a problem with adding and subtracting. You can change this subtraction (in the middle) by using "Add the Opposite". Remember to change both pieces of the second parenthesis to the opposite.
7x - y + -7x - 9y
If you need to see it, rearrange putting the LIKE terms together.
7x + -7x - y - 9y
The x's add up to 0.
-y - 9y
gives you -10y
