The entire circle has a central angle of 360°.
Because the radius is 6 mi, the area of the circle is
π(6)² = 36π mi².
The sector has a central angle of 60°, therefore it occupies 60/360 = 1/6 of the area of the circle.
The area of the sector is
(1/6)*36π = 6π mi² = 18.85 mi²
Answer: 6π mi² or 18.85 mi².