A runway is 105 meters long. Gu Qing ran 4 times back and forth. How many meters did he run in total?
一条跑道长105米，顾青跑4个来回，一共跑了多少米．
<gadget id="calculator">4 * 2</gadget>
<output>8</output>

<gadget id="calculator">105 * 8</gadget>
<output>840</output>

<result>840</result>