Fill in 5 in the latter term of 8:5, how much should be added to the former term to keep the ratio unchanged
给8：5的后项填上5，要使比值不变，前项应该加上多少
<gadget id="calculator">5 + 5</gadget>
<output>10</output>

<gadget id="calculator">10 / 5</gadget>
<output>2</output>

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

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

<result>8</result>