The formula for the area of a circle is PI x radius^2
The park has a radius of 200m
The area of the park = PI x 200^2 = 125,600 square meters.
The radius of the fountain is 10m
The area of the fountain = PI x 10^2 = 314 square meters.
The area to walk ids the area of the park minus the area of the fountain:
125,600 - 314 = 125,286 square meters.