3 times of X plus itself is equal to 2.8, find X.
X的3倍加上它的本身等于2.8，求X．
<gadget id="calculator">3 + 1</gadget>
<output>4</output>

<gadget id="calculator">2.8 / 4</gadget>
<output>0.7</output>

<result>0.7</result>