5: Add 1 to the front item of 8, to keep the ratio unchanged, how much should be added later
5：8的前项加l，要使比值不变，后相应加多少
<gadget id="calculator">5 + 1</gadget>
<output>6</output>

<gadget id="calculator">6 / 5</gadget>
<output>6/5 = around 1.2</output>

<gadget id="calculator">8 * (6/5)</gadget>
<output>48/5 = around 9.6</output>

<gadget id="calculator">(48/5) - 8</gadget>
<output>8/5 = around 1.6</output>

<result>8/5 = around 1.6</result>