Answer: He ran 8 miles on week 5, which was an improvement of 6.4 miles compared to the 1.6 miles he ran on the first week,
Explanation:
In the fifth week, the ratio of the number of miles he ran to the number of miles he walked improved to 8:5
Nash ran 8 miles in 5 weeks.
In 1 week he ran 1.6 miles
8 - 1.6 = 6.4