Solve the equation: 3(x+3)=18.
解方程：3(x+3)=18．
<gadget id="calculator">3 * 3</gadget>
<output>9</output>

<gadget id="calculator">18 - 9</gadget>
<output>9</output>

<gadget id="calculator">9 / 3</gadget>
<output>3</output>

<result>3</result>