What is the perimeter of a semicircle with a radius of 6dm?
半径是6dm的半圆，它的周长是多少．
<gadget id="calculator">3.14 / 2</gadget>
<output>1.57</output>

<gadget id="calculator">2 * 6 * 1.57</gadget>
<output>18.84</output>

<gadget id="calculator">6 * 2</gadget>
<output>12</output>

<gadget id="calculator">18.84 + 12</gadget>
<output>30.84</output>

<result>30.84</result>