If the area of a triangle is 21 square meters, what is the area of a parallelogram with the same base and height in square meters?
一个三角形的面积是21平方米，和它等底等高的平行四边形的面积是多少平方米．
<gadget id="calculator">21 * 2</gadget>
<output>42</output>

<result>42</result>