Beibei and Niuniu are racing on the playground. Beibei runs 6 meters per second, and it takes 21 seconds to complete a lap; Niuniu wants to complete a lap 3 seconds faster than Beibei, how many meters per second does she need to run?
贝贝和妞妞在操场上比赛跑步，贝贝每秒跑6米，跑完一圈要21秒；妞妞想比贝贝快3秒跑完一圈，每秒需跑多少米？
<gadget id="calculator">21 - 3</gadget>
<output>18</output>

<gadget id="calculator">21 / 18</gadget>
<output>7/6 = around 1.166667</output>

<gadget id="calculator">6 * (7/6)</gadget>
<output>7</output>

<result>7</result>