Chen Ping drew a rectangle with a perimeter of 40 cm, and the length is three times the width. What is the area of this rectangle?
陈平画了一个周长是40厘米的长方形，其中长是宽的3倍，这个长方形的面积是多少？
<gadget id="calculator">1 + 3</gadget>
<output>4</output>

<gadget id="calculator">40 / 2 / 4</gadget>
<output>5</output>

<gadget id="calculator">3 * 5</gadget>
<output>15</output>

<gadget id="calculator">15 * 5</gadget>
<output>75</output>

<result>75</result>