4: 4 is added to the former term of 5, to keep the ratio unchanged, how much should be added to the latter term of the ratio
4：5的前项加上4，要使比值不变，比的后项应加上多少
<gadget id="calculator">4 + 4</gadget>
<output>8</output>

<gadget id="calculator">8 / 4</gadget>
<output>2</output>

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

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

<result>5</result>