x+7=7+x
(x+y)+z=x+(y+z)
x+x=2x
2x+2=12
x+y=y+x
3x=6
2x+4=2*(x+2)
2x+1=1
2x=6
x+3=2+2x
3+7x=9x-2x+3
x+4=8