16/21
 dresses
Step-by-step explanation:
The ratio of time required to dresses made is
3/4•k hours: 4/7 • k dresses for any constant k.
Specifically, if we want 1 hour then the letter K will need to be 4/3.
 .
So 
4/7 x 3/4= 16/21 in an hour. 
I hope this make sense LOL!