A bit difficult problem

[kate]

Three snails go one after the other from one point in the same direction. Their speeds are: the first snail's speed is - 4 cm per second, the second - 5 cm per minute, and the third - 6 ck per minute. The second snail went 3 hours after the first one. How many hours after the second one should the third snail go, in order to reach the first snail together with the second?