Explanation:
To begin, we will convert the measurements of the enlarged poster to inches, so as to be able to compare inches with inches.
1 ft = 12 inches
2 ft = 24 inches
The shorter side in the original poster was 4, now it is 12. The longer side was 8, now it is 24.
12/4 = 3
24/8 = 2
Answer: scale factor = 3 inches
