The physical education teacher draws a set of 50-meter-long tracks for 4-person group competitions. It took the teacher 3 minutes to draw each runway line, how many minutes did it take to draw this group of runways?
体育老师画一组供4人小组赛的50米长的跑道．老师画完每条跑道线用3分钟，画完这组跑道共用多少分钟？
<gadget id="calculator">4 + 1</gadget>
<output>5</output>

<gadget id="calculator">5 * 3</gadget>
<output>15</output>

<result>15</result>