8: The former term of 15 is increased by 8, how much should the latter term be increased to keep the ratio unchanged.
8：15的前项增加8，要使比值不变，后项应增加多少．
<gadget id="calculator">8 + 8</gadget>
<output>16</output>

<gadget id="calculator">16 / 8</gadget>
<output>2</output>

<gadget id="calculator">2 * 15</gadget>
<output>30</output>

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

<result>15</result>