The original area of a rectangular park is 15 hectares. Now the length of the park is expanded to 3 times the original size, and the width remains unchanged. What is the area of the park after the expansion?
一个长方形公园原来的面积是15公顷，现在将这个公园的长扩大到原来的3倍，宽不变，扩建后公园的面积是多少公顷．
<gadget id="calculator">15 * 3</gadget>
<output>45</output>

<result>45</result>