The perimeter of an isosceles trapezoid is 30 cm, the upper base, waist and height are 7.5 cm, 5 cm and 3.6 cm respectively. What is the area of this trapezoid?
有一等腰梯形的周长是30厘米，上底、腰和高分别是7.5厘米、5厘米和3.6厘米，求这个梯形的面积是多少？
<gadget id="calculator">5 * 2</gadget>
<output>10</output>

<gadget id="calculator">30 - 7.5 - 10</gadget>
<output>12.5</output>

<gadget id="calculator">7.5 + 12.5</gadget>
<output>20</output>

<gadget id="calculator">3.6 / 2</gadget>
<output>1.8</output>

<gadget id="calculator">20 * 1.8</gadget>
<output>36</output>

<result>36</result>