-12+(4-7) =
(-3)+(-3)-(-3) =
15-(16-12+25) =
-(4-7)+(5-12) =
-(-6)-(+6)+(-6) =
-(5x-4)-7 =
2x-(x-5) =
(2a-3)-(7a-5) =
(a-5)-(a-7)+(a-9) =
5x-(2x-3y-5) =

wb 56, nr. 9