67.2 minutes
First convert the runner's speed from mi/h to km/h by multiplying by 1.60934 km/mi, giving
7.1 mi/h * 1.60934 km/mi = 11.43 km/h
Divide the distance by her speed.
12.8 km / (11.43 km/h) = 1.12 h
Convert hours to minutes by multiplying by 60
1.12 h * 60 min/h = 67.2 min