It is known that

$$1hour=60minutes$$ It is given that Katerina runs 15 miles in $2\frac{1}{2}$ hours, thus she runs 1 mile in

$$\frac{2\frac{1}{2}}{15}hours$$

To convert hours into minutes, we multiple by 60:

$$\frac{2\frac{1}{2}}{15}\times 60=10minutes$$