Since Katie continued to travel in the 15 minutes after she passed the milestone, the distance she traveled in that 15 minutes is
\(15 minutes * \frac{1 hour }{ 60 minutes} * 50 miles per hour = 12.5 miles\)
Let h = time in hours after Jack passed the milestone.
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There are 2 ways that the distance between Jack and Katie equals 10 miles:
1) Jack is behind Katie by 10 miles\(60h + 10 = 12.5 + 50h\)
\(10h = 2.5\)
\(h = \frac{2.5}{10} = \frac{1}{4}\)
Multiply by 60 to get 15 minutes.
2) Katie is behind Jack by 10 miles (since Jack's speed is faster, he will eventually surpass her)\(60h = 12.5 + 10 + 50h\)
\(10h = 22.5\)
\(h = 2.25\)
Multiply by 60 to get 135 minutes.