If A:B=5:4, the number of A increases by 20, how much should the number of B increase to keep the ratio constant
如果甲：乙=5：4，甲数增加20，要使比值不变，乙数应增加多少
<gadget id="calculator">5 * 4</gadget>
<output>20</output>

<gadget id="calculator">20 - 4</gadget>
<output>16</output>

<result>16</result>