The school breeding group raises white rabbits and gray rabbits. There are 4 gray rabbits in every 9 rabbits. There are 20 white rabbits. How many gray rabbits are there?
学校饲养组养了白兔和灰兔，每9只兔子中有4只灰兔，白兔有20只，灰兔有多少只？
<gadget id="calculator">9 - 4</gadget>
<output>5</output>

<gadget id="calculator">20 / 5</gadget>
<output>4</output>

<gadget id="calculator">4 * 4</gadget>
<output>16</output>

<result>16</result>