The perimeter of a rectangle is 84 cm, and the ratio of length to width is 3:1. What is the area of the rectangle in square centimeters?
一个长方形的周长是84厘米，长、宽的比是3：1，这个长方形的面积是多少平方厘米？
<gadget id="calculator">63 / 2</gadget>
<output>63/2 = around 31.5</output>

<gadget id="calculator">21 / 2</gadget>
<output>21/2 = around 10.5</output>

<gadget id="calculator">(63/2) * (21/2)</gadget>
<output>1_323/4 = around 330.75</output>

<result>1_323/4 = around 330.75</result>