The upper base of a trapezoid is 3 cm, the lower base is twice the upper base, and the height is 1.5 times the lower base. What is the area of the trapezoid in square centimeters?
一个梯形的上底是3厘米，下底是上底的2倍，高是下底的1.5倍，这个梯形的面积是多少平方厘米．
<gadget id="calculator">3 * 2</gadget>
<output>6</output>

<gadget id="calculator">3 + 6</gadget>
<output>9</output>

<gadget id="calculator">6 * 1.5</gadget>
<output>9</output>

<gadget id="calculator">9 / 2</gadget>
<output>9/2 = around 4.5</output>

<gadget id="calculator">9 * (9/2)</gadget>
<output>81/2 = around 40.5</output>

<result>81/2 = around 40.5</result>