Area of the circle
The are of a circle is given by:

Where:
π = 3.14159
r = radius of the circle
In our problem we have:
r = 5
So, applying the formula of above we find that:

Circle Area = 78.5 mi²
Area of the sector area of the circle
We can calculate the area of a sector of a circle using the following formula:

Where:
θ = angle of the sector
In our problem we have:
θ = 60°
So, applying the formula of above we find that:

Sector Area = 13.1 mi²