The inner term 3 of the ratio 5:3=15:9 is increased by 6, how much should the outer term 9 be increased to make the ratio valid
比例5：3=15：9的内项3增加6，要使比例成立，外项9应该增加多少
<gadget id="calculator">3 + 6</gadget>
<output>9</output>

<gadget id="calculator">15 / 5</gadget>
<output>3</output>

<gadget id="calculator">9 * 3</gadget>
<output>27</output>

<gadget id="calculator">27 - 9</gadget>
<output>18</output>

<result>18</result>