(4.5X+31.5)÷X=(4.5X-31.5)÷(X-12)
两边都除以4.5,约分后得
(X+7)÷X=(X-7)÷(X-12)
然后交叉相乘得
(X+7)*(X-12)=X*(X-7)
得2X=84 所以X=42