Error in Solutions Manual
The Solutions Manual has the answer from the older version of the book (which used a flag of 104 x 235. Flags have grown since then. 😉)
Just FYI – the older flag was flown in Detroit on the side of the J.L. Hudson Store – which no longer exists.
See it here: Worlds Largest Flag
Answer to a) Perimeter, 1520 feet; Area, 128,775 square feet
Answer to b) Perimeter, 1524 feet; Area, 129,536 square feet
Answer to c) Perimeter, (1520 + 4x) feet; Area, (128,775 + 760x + x^2)