Answer:
-81
If (4x + 5x)-(4y-7y) -81 - 3y) then, it will become 9 (x - 9).
Why will it become 9 (x - 9)? :
>4x + 5x - 4y + 7y - 81 - 3y
>9x + 0 -81
>9x - 81
= 9 (x - 9)
Solution for the -81 :
Solve for x first:
>(4x + 5x)-(4y-7y)___- 3y
>(9x) - (-3y) ___-3y
>(9x) + 3y - 3y ____
>9x (transpose, becomes negative)
x= -9
Replace the x to -9:
>(4(-9) + 5(-9))-(4y-7y)___- 3y
>(-36 - 45) - (-3y) - 3y
>(-81) + 3y - 3y
= -81
