x/5-x=-10-70x（1/5-1）=-80-4/5x=804/5x=804x=400x=100
x/5+80=x两边同乘以5得X+400=5X 400=4X X=100
x/5+10+70=x4x/5=80x=100
x-x/5=804x/5=80x=100
x/5+120=x x-x/5=120 4x/5=120 x=120*5/4=150
