The area of a rectangular park is 15 hectares. The length of the park is doubled and the width remains the same. What is the area of the park after expansion
一个长方形公园的面积是15公顷，将公园的长扩大到原来的2倍，宽不变．扩建后公园的面积是多少公顷
<gadget id="calculator">15 * 2</gadget>
<output>30</output>

<result>30</result>