What is the difference in circumference between a circle with a radius of 3 cm and a semicircle with a radius of 3 cm?
一个半径3厘米的圆和一个半径3厘米的半圆，周长相差多少．
<gadget id="calculator">3.14 * 3 * 2</gadget>
<output>18.84</output>

<gadget id="calculator">3.14 * 3</gadget>
<output>9.42</output>

<gadget id="calculator">2 * 3</gadget>
<output>6</output>

<gadget id="calculator">9.42 + 6</gadget>
<output>15.42</output>

<gadget id="calculator">18.84 - 15.42</gadget>
<output>3.42</output>

<result>3.42</result>