A right-angled trapezoid, the sum of the upper and lower bases is 18 cm, and the lengths of the two sides are 4 cm and 6 cm respectively. What is the area of the trapezoid in square centimeters?
一个直角梯形，上下底的和是18厘米，两腰分别长4厘米和6厘米，这个梯形的面积多少平方厘米？
<gadget id="calculator">4 / 2</gadget>
<output>2</output>

<gadget id="calculator">18 * 2</gadget>
<output>36</output>

<result>36</result>