The perimeter of an isosceles trapezoid is 50 cm, the waist and height are 10 cm and 8 cm, respectively. What is the area of this trapezoid?
一个等腰梯形的周长是50cm，腰和高分别为10cm和8cm．这个梯形的面积是多少？
<gadget id="calculator">10 * 2</gadget>
<output>20</output>

<gadget id="calculator">50 - 20</gadget>
<output>30</output>

<gadget id="calculator">8 / 2</gadget>
<output>4</output>

<gadget id="calculator">30 * 4</gadget>
<output>120</output>

<result>120</result>