Cut the largest semicircle out of a rectangular paper with a length of 30 cm and a width of 10 cm. What is the area of the semicircle?
在一张长30厘米、宽10厘米的长方形纸里剪下一个最大的半圆，这个半圆的面积是多少？
<gadget id="calculator">10 ** 2</gadget>
<output>100</output>

<gadget id="calculator">100 / 2</gadget>
<output>50</output>

<gadget id="calculator">3.14 * 50</gadget>
<output>157</output>

<result>157</result>