A butterfly flies 3.9 kilometers at 0.5 hours, and a bee flies about twice as fast as the butterfly. How many kilometers does the bee fly per hour?
一只蝴蝶0.5时飞行3.9千米，一只蜜蜂的飞行速度约是这只蝴蝶的2倍，这只蜜蜂每小时飞行多少千米？
<gadget id="calculator">3.9 / 0.5</gadget>
<output>7.8</output>

<gadget id="calculator">7.8 * 2</gadget>
<output>15.6</output>

<result>15.6</result>