If 10 is added to the former term of 5:7, how much should be added to the latter term to keep the ratio constant
若5：7的前项加上10，要使比值不变，后项应加上多少
<gadget id="calculator">5 + 10</gadget>
<output>15</output>

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

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

<gadget id="calculator">21 - 7</gadget>
<output>14</output>

<result>14</result>