If a concentric circle with a radius of 10 cm is cut out of a circle with a diameter of 4 decimeters, what is the area of the remaining part?
一个直径为4分米的圆中，挖掉一个半径为10厘米的同心圆，剩下部分的面积是多少．
<gadget id="calculator">400 - 100</gadget>
<output>300</output>

<gadget id="calculator">3.14 * 300</gadget>
<output>942</output>

<result>942</result>