The central angle of a sector is 90°, and its perimeter is 14.28 cm. Find its area.
一个扇形的圆心角是90°，它的周长是14.28厘米，求它的面积．
<gadget id="calculator">4 ** 2</gadget>
<output>16</output>

<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">3.14 * 16 * (1/4)</gadget>
<output>12.56</output>

<result>12.56</result>