You are not given m, you are given value of m2/3t1/6 combined, just as a thing to put into the equation:
15.2 = 607*2*D1/2*1.66*2.10
This combined value (containing both speed of mercury flowing and droplet lifetime in correct powers) has units kg2/3s-1/2
(note that equation as shown is correct only in general, I am not sure about mili/micro factors; also note that I have translated Polish terms into English without checking them, so I can be completely off with the established nomenclature).