A fast horse travels 240 miles a day, a slow horse travels 150 miles a day, a slow horse goes first for 12 days, how many days does it take for a fast horse to catch up with a slow horse?
跑得快的马每天行240里，跑得慢的马每天行150里，慢马先行12天，快马几天可追上慢马？
<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>