The base of a parallelogram is 21 decimeters and the height is twice the base. What is the area of the parallelogram in square decimeters?
一个平行四边形的底是21分米，高是底的2倍，这个平行四边形的面积是多少平方分米．
<gadget id="calculator">21 * 2</gadget>
<output>42</output>

<gadget id="calculator">21 * 42</gadget>
<output>882</output>

<result>882</result>