The ratio of the length to the width of a rectangle is 4:3, its perimeter is known to be 42 cm, what is its area in square centimeters?
一个长方形长和宽的比是4：3，已知它的周长是42cm，试求它的面积是多少平方厘米？
<gadget id="calculator">42 / 2</gadget>
<output>21</output>

<gadget id="calculator">4 + 3</gadget>
<output>7</output>

<gadget id="calculator">4 / 7</gadget>
<output>4/7 = around 0.571429</output>

<gadget id="calculator">21 * (4/7)</gadget>
<output>12</output>

<gadget id="calculator">3 / 7</gadget>
<output>3/7 = around 0.428571</output>

<gadget id="calculator">21 * (3/7)</gadget>
<output>9</output>

<gadget id="calculator">12 * 9</gadget>
<output>108</output>

<result>108</result>