The ratio of length to width of a rectangle is 4:3, and its perimeter is 21 cm. What is its area in square centimeters?
一个长方形的长宽之比是4：3，周长是21厘米，它的面积是多少平方厘米．
<gadget id="calculator">21 / 2</gadget>
<output>21/2 = around 10.5</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">(21/2) * (4/7)</gadget>
<output>6</output>

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

<gadget id="calculator">(21/2) * (3/7)</gadget>
<output>9/2 = around 4.5</output>

<gadget id="calculator">6 * (9/2)</gadget>
<output>27</output>

<result>27</result>