The perimeter of an isosceles trapezoid is 40 decimeters, the height is 5 decimeters, and the length of one side is 8 decimeters. What is the area of this isosceles trapezoid?
一个等腰梯形的周长是40分米，高是5分米，一条腰长8分米，这个等腰梯形的面积是多少平方分米．
<gadget id="calculator">8 * 2</gadget>
<output>16</output>

<gadget id="calculator">40 - 16</gadget>
<output>24</output>

<gadget id="calculator">5 / 2</gadget>
<output>5/2 = around 2.5</output>

<gadget id="calculator">24 * (5/2)</gadget>
<output>60</output>

<result>60</result>