A trapezoidal plastic plate, the upper base is 15 cm long, the lower base is three times as long as the upper base, and the height is 12 cm. What is the area of this plastic plate?
一个梯形塑料板，上底长15厘米，下底长是上底的3倍，高是12厘米，这块塑料板的面积是多少？
<gadget id="calculator">15 * 3</gadget>
<output>45</output>

<gadget id="calculator">15 + 45</gadget>
<output>60</output>

<gadget id="calculator">12 / 2</gadget>
<output>6</output>

<gadget id="calculator">60 * 6</gadget>
<output>360</output>

<result>360</result>