A triangle has the same height and area as a parallelogram. The base of the parallelogram is 15 cm. What is the length of the base of the triangle in cm?
一个三角形与一个平行四边形的高相等，面积也相等，平行四边形的底15cm，三角形的底长多少cm．
<gadget id="calculator">15 * 2</gadget>
<output>30</output>

<result>30</result>