3+8+x:2=2x+13

3+8+x/2=2x+13 12+x/2=2x+13 x/2=2x+13 /×2 x=4x+2 x=-2/5

11+x:2=2x+13 -2x+x:2=13-11 -2x+x:2=2 -2x+x=4 -x=4 x=-4

3+8+x=4x+26 11+x=4x+26/-11 x=4x+15/-4x -3x=15/:(-3) x=-5