suppose a runner completes a 10k (10.0km) road.race in 43 minutes and 55 seconds what is the runners average speed in miles per hour

Answer 1

10 km = 6.21371 mi
53 sec = 53/60 min = 53/3600 h

10 km/(43 min and 53 sec) = 6.213671 mi/(43/60 + 53/3600 h)
You can find the answer on the calculator.

Answer 2

I wouldn't call this a chemistry question.