Answer:
Mathew runs in 3rd week = 14.58 miles
Explanation:
Mathew is training to participate in a half marathon.
In week 1 he runs 12.5 miles.
Similarly he runs 13.5 miles in week 2.
So the difference in distance he runs from week 1 to week 2 is
13.5 - 12.5 = 1 mile
Now % difference in distance from week 1 to week 2
=

= 8%
Now it is given in the question that Mathew increases the same percent of distance to run in every successive week.
So increase of distance in third week = 8% of 13.5 miles
=
miles
Distance to run in 3rd week = 13.5 + 1.08 = 14.58 miles