Due to the circular shape, one complete rotation of the flag is equal to the circumference of a circle with radius 12 ft.
Then, use the following formula for the cirumference:
C = 2π·r
where r is the radius. In this case, r = 12 ft and π = 3.14. Replace the previous values into the formula for C:
C = 2(3.14)(12 ft)
C = 75.36 ft
Hence, the flag has to travel 75.36 ft to complete a full rotation