x+(7/8)*(x+21)+x+21=4x
x+x+21+(7/8)*(x+21)=4x
2x+21+(7/8)*(x+21)=4x
21+(7/8)*(x+21)=2x
168+7(x+21)=16x
168+7x+147=16x
16x-7x=315
9x=315
x=35
x+(7/8)*(x+21)+x+21=4x
x+x+21+(7/8)*(x+21)=4x
2x+21+(7/8)*(x+21)=4x
21+(7/8)*(x+21)=2x
168+7(x+21)=16x
168+7x+147=16x
16x-7x=315
9x=315
x=35