From the title, we know that the flying time of butterflies is 0.4 hours and the distance is 3 kilometers. So we can know that the speed of the butterfly is: distance divided by time, that is:

3 meters /0.4 hour =7.5 kilometers/hour.

Then the speed of bees is 2.4 times that of butterflies, so we know that the speed of bees is: 2.4 * 7.5 =18km/h.

So the answer is: 18 kilometers per hour.