Use an iron wire with a length of 7.54 decimeters to surround a quarter circle with a knot of 4 centimeters. How big is the enclosed area?
用一根长7.54分米的铁丝，围一个四分之一圆，结头处4厘米，围成的面积有多大？
<gadget id="calculator">75.4 - 4</gadget>
<output>71.4</output>

<gadget id="calculator">2 / 4</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">3.14 * (1/2)</gadget>
<output>1.57</output>

<gadget id="calculator">2 + 1.57</gadget>
<output>3.57</output>

<gadget id="calculator">71.4 / 3.57</gadget>
<output>20</output>

<gadget id="calculator">20 ** 2</gadget>
<output>400</output>

<gadget id="calculator">400 / 4</gadget>
<output>100</output>

<gadget id="calculator">3.14 * 100</gadget>
<output>314</output>

<result>314</result>