There are the same red balls and white balls in the box. Take out 9 red balls and 4 white balls each time. After taking out several times, the red balls are gone, and there are 20 white balls left. How many red balls and white balls are there?
箱子里装有同样的红球和白球，每次取出9个红球，4个白球，取出几次后红球没有了，白球还剩20个，原来红球和白球各有多少个？
<gadget id="calculator">9 - 4</gadget>
<output>5</output>

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

<gadget id="calculator">4 * 9</gadget>
<output>36</output>

<result>36</result>