6.
a+4a=5a
7a+3(a+7)=7a+3a+21=10a+21
8(a+b)+3(a-b)=8a+8b+3a-3b=11a+5b
9x-4-x+5(x+y+2)=9x-4-x+5x+5y+10=13x+5y-6
a+2(a+2)=a+2a+4=3a+4
4(a+5)+5(a+6)=4a+20+5a+30=9a+50
x+5y+3(x+y)=x+5y+3x+3y=4x+8y
7x-4x=3x
8x+3x-x=10x
6y-y=5y
9y+2y-4y=7y
