As given that The thickness of the wall = 30cm = 0.3m. Length of long wall = 3 × 6 = 18m. And, Now, Length of sort wall = [(2 × 4) + (2 × 0.3 × 2) + (2 × 3) + (2 × 0.3) + 0.3] = [8 + 1.2 + 6 + 0.6 + 0.3] = 16.1m. Hence, the total center line length for the given plan = 18 + 16.1 = 34.1m.