There are two kinds of colored balls, red and white, and the red balls account for (9/20). If 16 white balls are added, the ratio of red and white balls is 1:3. How many red balls are there?
有红、白两种彩球放在一起，其中红球占(9/20)，如再放入16个白球，则红、白球个数的比是1：3，红球有多少个？
<gadget id="calculator">20 - 9</gadget>
<output>11</output>

<gadget id="calculator">11 / 9</gadget>
<output>11/9 = around 1.222222</output>

<gadget id="calculator">3 - (11/9)</gadget>
<output>16/9 = around 1.777778</output>

<gadget id="calculator">16 / (16/9)</gadget>
<output>9</output>

<result>9</result>