Question 988747
The error is going from 4x-(3y+7x) to 4x-3y+7x


the negative out front of the (3y+7x) isn't properly distributed through


EVERY term inside must change in sign. The 3y changes to -3y, which is good. But the 7x doesn't change in sign. The 7x should turn into -7x


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Correct simplification


4x-(3y+7x)
4x-3y-7x
4x-7x-3y
(4x-7x)-3y
-3x-3y


In the end, 4x-(3y+7x) simplifies to -3x-3y