em 2 L 5.1.2 Exam: Semester Exam Use the given scale factor and the side lengths of the scale drawing to determine the side lengths of the real object. Scale factor: 3:1 18 in b a 21 in Scale drawing Object O A. Side a is 18 inches long and side bis 15 inches long. O B. Side a is 63 inches long and side bis 54 inches long. C. Side a is 7 inches long and side bis 6 inches long. O D. Side a is 24 inches long and side bis 21 inches long.​