so if you mean 35 day to 7 weeks in proportion
one way is to divide 35 and 7 by 7 and get 5 days to 1 week or 5 days to 7 days or 5:7
or you could convert to the same unit (days)
1 week=7 days
7 weeks=49 days (7 times 7)
35:49
factor
35=5 times 7
49=7 times 7
so factor out the 7 and get
5:7 days