There is a street light every 50m on one side of the road. Ning Ning saw the 21st street light when he saw the 21st street light when he took the trolleybus and counted 2 minutes from the first street light. How many kilometers does the trolleybus travel per hour?
公路的一侧每隔50m有一盏路灯，宁宁乘无轨电车从看到第一盏路灯开始计时2分针时看到第21盏路灯，问无轨电车每小时行驶多少千米？
<gadget id="calculator">21 - 1</gadget>
<output>20</output>

<gadget id="calculator">50 / 2</gadget>
<output>25</output>

<gadget id="calculator">60 / 1_000</gadget>
<output>3/50 = around 0.06</output>

<gadget id="calculator">20 * 25 * (3/50)</gadget>
<output>30</output>

<result>30</result>