Mary ran the 5 kilometre race in 45 minutes. Melanie ran the 2 kilometre race in 17 minutes. Which runner ran the faster race? What was that rate per hour

Mary ran the 5 kilometre race in 45 minutes.

45 minutes = 3/4 of an hour

This means that her speed is

S/t=5 / (3/4) = 20/3 = 6+2/3 (km / hour)

Melanie ran the 2 kilometre race in 17 minutes.

17 minutes = 17/60 of an hour

This means that her speed is

S/t=2 / (17/60) = 120/17 = 7+1/17 (km / hour)

So, Melanie is faster than Mary.