You simply have to convert both to the same unit otherwise the answer will be meaningless.
You will either convert 1500 miles to 2400km
(I assume you mean statute not nm)
or 200kph to 125mph
then divide the distance by the speed...
either way you get 12hrs
I don't know a site which will do the whole thing but I am sure a google search would get you a site that would enable you to convert everything to the same unit.
I have a question for you now - why am I answering this on a Friday night? I should be down the pub!
