A piece of triangular glass has a base of 20 cm and a height twice that of the base. What is its area in cm**2?
一块三角形玻璃，底是20厘米，高是底的2倍，它的面积是多少cm**2？
<gadget id="calculator">20 * 2</gadget>
<output>40</output>

<gadget id="calculator">40 / 2</gadget>
<output>20</output>

<gadget id="calculator">20 * 20</gadget>
<output>400</output>

<result>400</result>