Explanation:
I am not sure I understand the question with all the typos and potentially missing parts.
as I understand it, it will take her 4 hours to reach her destination when going 15 mph.
and the question is how long the trip will take, if she travels at 12 mph.
4 h × 15 m/h = 4 × 15 m = 60 miles
that is the distance of her trip.
when going slower, the distance is of course still the same, only the needed time changes :
x h × 12 m/h = 60 m
x × 12 m = 60 m
x = 60/12 = 5 hours
the trip would take her 5 hours to complete (instead of 4).