(m+n)-(m-n)=
(m+3)-(6m+5)-(m-1)=
(x-y)+(x-y)-(2x+y)=
(m+n)-(m-n)=m+n-m+n=2n
(m+3)-(6m+5)-(m-1)=m+3-6m-5-m+1=-6m-1
(x-y)+(x-y)-(2x+y)=x-y+x-y-2x-y=-3y
1)=m+n-m+n=2n
2)=m+3-6m-5-m+1=-6m-1
3)=x-y+x-y-2x-y=-3y