Answer: 1/4
Explanation:
The question is indirectly asking for the number of weeks he spent to complete his ride.
1 week = 7days , then
91 days = 91/7 weeks
= 13 weeks
So the fraction in simplest form represents the part of a year, in week, he took to complete this ride will be the weeks spent / the total weeks in a year, that is
13/52
= 1/4