8: Add 16 to the former item of 15, how much should be added to the latter item to keep the ratio unchanged.
8：15的前项加上16，要使比值不变，后项应该加上多少．
<gadget id="calculator">15 * 3</gadget>
<output>45</output>

<gadget id="calculator">45 - 15</gadget>
<output>30</output>

<result>30</result>