Answer:
The minimum height of the flag is 9 feet.
Explanation:
The function representing the height of the flag is given by,

It is required to find the minimum height of the flag.
As, we know,
The function
have values between [-1,1] for all values of t.
So,
have values between [-1,1] for all values of t.
Then,
have values between [-3,3] for all values of t.
Thus,
have values between [-3+12,3+12] for all values of t.
That is,
have values between [9,15] for all values of t.
Hence, the minimum height of the flag is 9 feet.