We have,
8 m 25cm = 825cm,
6m 75cm = 675cm
4 m 50 cm = 450 cm
Length of the longest rod in cm is the HCF of 825, 675 and 450.
825 = 3 × 5 × 5 × 11
675 = 3 × 3 × 3 × 5 × 5
450 = 2 × 3 × 3 × 5 × 5
HCF (825, 675 and 450) = 3 × 5 × 5 = 75
Hence, the required length of rod = 75 cm