The perimeter of a rectangle is 40 cm, and the ratio of length to width is 7:3, what is the area of the rectangle in square centimeters?
一个长方形的周长是40厘米，已知长和宽的比是7：3，这个长方形的面积是多少平方厘米．
<gadget id="calculator">40 / 2</gadget>
<output>20</output>

<gadget id="calculator">7 + 3</gadget>
<output>10</output>

<gadget id="calculator">7 / 10</gadget>
<output>7/10 = around 0.7</output>

<gadget id="calculator">20 * (7/10)</gadget>
<output>14</output>

<gadget id="calculator">20 - 14</gadget>
<output>6</output>

<gadget id="calculator">14 * 6</gadget>
<output>84</output>

<result>84</result>