5: Add 14 to the latter term of 7, how much should be added to the former term to keep the ratio unchanged.
5：7的后项加上14，要使比值不变，前项应加上多少．
<gadget id="calculator">7 + 14</gadget>
<output>21</output>

<gadget id="calculator">21 / 7</gadget>
<output>3</output>

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

<gadget id="calculator">15 - 5</gadget>
<output>10</output>

<result>10</result>