Four times a number minus half of the number, the difference is 12.6, what is the number
一个数的4倍减去这个数的一半，差是12.6，这个数是多少
<gadget id="calculator">4 - 0.5</gadget>
<output>3.5</output>

<gadget id="calculator">12.6 / 3.5</gadget>
<output>3.6</output>

<result>3.6</result>