Subtract 5.8 from twice a number to get 2. Find this number.
一个数的2倍减去5.8得2，求这个数．
<gadget id="calculator">2 + 5.8</gadget>
<output>7.8</output>

<gadget id="calculator">7.8 / 2</gadget>
<output>3.9</output>

<result>3.9</result>