A good horse travels 240 miles a day, a bad horse travels 150 miles a day, and a bad horse travels for 12 days first. How many days can a good horse chase a bad horse? Use two methods of solving equations and calculating formulas.
好马每天走240里，劣马每天走150里，劣马先走12天，好马几天可以追是劣马？使用解方程和算式两种方法．
<gadget id="calculator">240 - 150</gadget>
<output>90</output>

<gadget id="calculator">12 / 90</gadget>
<output>2/15 = around 0.133333</output>

<gadget id="calculator">150 * (2/15)</gadget>
<output>20</output>

<result>20</result>