Two gears mesh with each other. The large gear has 80 teeth and the speed is 90 rpm. The speed of the small gear is 4 times that of the large gear. How many teeth does the small gear have?
两个互相咬合的齿轮，大齿轮有80个齿，转速为90转/分，小齿轮的转速是大齿轮的4倍，小齿轮有多少个齿？
<gadget id="calculator">80 * 90</gadget>
<output>7_200</output>

<gadget id="calculator">90 * 4</gadget>
<output>360</output>

<gadget id="calculator">7_200 / 360</gadget>
<output>20</output>

<result>20</result>