A rectangular plank is 6 decimeters long and 4 decimeters wide, cut off the largest semicircular plank from above, find the area of the semicircular plank.
一块长方形木板长6分米，宽4分米，从上面截下一块最大的半圆形木板，求半圆形木板的面积．
<gadget id="calculator">6 / 2</gadget>
<output>3</output>

<gadget id="calculator">3 ** 2</gadget>
<output>9</output>

<gadget id="calculator">9 / 2</gadget>
<output>9/2 = around 4.5</output>

<gadget id="calculator">3.14 * (9/2)</gadget>
<output>14.13</output>

<result>14.13</result>