A trapezoidal experimental field, the upper base is 15m, the lower base is three times the upper base, and the height is 18m, what is the area of this experimental field in m**2?
一块梯形实验田，上底是15m，下底是上底的3倍，高是18m，这块实验田的面积是多少m**2？
<gadget id="calculator">15 * 3</gadget>
<output>45</output>

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

<gadget id="calculator">18 / 2</gadget>
<output>9</output>

<gadget id="calculator">60 * 9</gadget>
<output>540</output>

<result>540</result>