pake caranya y ..tolong!!

A) (42n + 35m + 7 ) - (-50m - 20n + 9)
   = 42n + 35m + 7 + 50m + 20n - 9
   = 35m + 50m + 42n + 20n + 7 - 9
   = 85m + 62n - 2

B) (5x + 3) - (x - 1)
   = 5x + 3 - x + 1
   = 5x - x + 3 + 1
   = 4x + 4

C) (2y + 15z) - (4y - 8)
   = 2y + 15z - 4y + 8
   = 2y - 4y + 15z + 8
   = -2y + 15z + 8

a. (42n+35m+7)-(-50m-20n+9)=42n+20n+35m+50m+7-9
                                                =22n+85m-2
b. (5x+3)-(x-1)=5x-x+3+1
                       =4x+4
c. (2y+15z)-(4y-8)=2y-4y+15z+8
                            =-2y+15z+8