Marcus painted 1/3 of his bedroom in 4/5 of an hour. at this rate, how long would it take him the paint the entire room? i need to now how to work it out

So it took him 4/5 of an  hour to paint 1/3 
that means there is still 2/3 to go 
so that means that he will have two times that time to paint the rest of the room
4/5    =  ? 
1/3       2/3 

using cross multiplication

(4/5)(2/3) = (1/3) (?)
8/15 = 1/3 ?
divide both sides by 1/3
so that will be 8/5
that means it will take 8/5 of an hour to complete the rest 
or 12/5 total to do entire room

Hope this helps ;)