Answer:
10 ft by 21.25 ft
Explanation:
Simply put, you just need to multiply both of the sides by 2.5 ft.
Since 1 cm = 2.5 ft, then 4 cm = 10 ft and 8 cm = 21.25
So your answer is 10 ft by 21.25 (The answer you selected is correct, btw)
Hope this helps! :D