The towers in case 1 can be covered in 3 frequencies.
The towers in case 2 can be covered in 2 frequencies.
The towers in case 3 can be covered in 3 frequencies.
The towers in case 4 can be covered in 3 frequencies.
The towers in case 5 can be covered in 1 frequencies.
The towers in case 6 can be covered in 2 frequencies.
The towers in case 7 can be covered in 3 frequencies.
The towers in case 8 can be covered in 4 frequencies.