A parallelogram has an area 21 square centimeters larger than that of a triangle with the same base and height. What is the area of the parallelogram in square centimeters?
一个平行四边形比与它等底等高的一个三角形的面积多21平方厘米，这个平行四边形的面积是多少平方厘米．
<gadget id="calculator">2 - 1</gadget>
<output>1</output>

<gadget id="calculator">21 / 1</gadget>
<output>21</output>

<gadget id="calculator">21 * 2</gadget>
<output>42</output>

<result>42</result>