A rectangle with a length of 31.2 cm is used to form a rectangle whose length is three times its width. What is the area of the rectangle?
用一根长31.2厘米的铁丝围成一个长方形，它的长是宽的3倍，这个长方形的面积是多少？
<gadget id="calculator">3 + 1</gadget>
<output>4</output>

<gadget id="calculator">31.2 / 2 / 4</gadget>
<output>3.9</output>

<gadget id="calculator">3.9 * 3 * 3.9</gadget>
<output>45.63</output>

<result>45.63</result>