The sum of 3 times x and 6 times x is 8.1, find x. (solution by equation)
x的3倍与x的6倍的和是8.1，求x．(用方程解)
<gadget id="calculator">3 + 6</gadget>
<output>9</output>

<gadget id="calculator">8.1 / 9</gadget>
<output>0.9</output>

<result>0.9</result>