A right-angled trapezoid has a perimeter of 45cm and two waists of 10cm and 5cm respectively. What is the area of this trapezoid?
一个直角梯形，周长是45cm，两个腰长分别是10cm、5cm，那么这个梯形的面积是多少？
<gadget id="calculator">45 - 10 - 5</gadget>
<output>30</output>

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

<gadget id="calculator">30 * (5/2)</gadget>
<output>75</output>

<result>75</result>