Xiao Ming runs 6 meters per second, and Xiao Ying runs 4 meters per second. Xiao Ming stands at the starting point of the 400-meter runway, and Xiao Ying stands 40 meters in front of him. The two start running in the same direction at the same time. After a few seconds, Xiao Ming catches up with Xiao Ying ? (solution by equation)
小明每秒跑6米，小颖每秒跑4米，小明站在400米跑道的起点处，小颖站在他前面40米处，两人同时同向起跑，几秒后小明追上小颖？(用方程解)
<gadget id="calculator">6 - 4</gadget>
<output>2</output>

<gadget id="calculator">40 / 2</gadget>
<output>20</output>

<result>20</result>