Answer:
A positive 3x
Explanation:
since both parts have the same variable you could add them or subtract them together
(3x-7x)+(3x+4x)
You will subtract 3x-7x which will give you a negative 4x
You will do the same on the other side
Add 3x+4x and it will give you a positive 7x
-4x+7x=will give you an positive 3x
Hopes this helps