Please submit your concern

Explanation:

When running in same direction, time taken for two trains to cross each other = $\frac{{\mathrm{L}}_1+{\mathrm{L}}_2}{\mathrm{f}-\mathrm{s}}$

L1 and L2 are the lengths of the two trains while f and s are the speeds of faster and slower trains respectively.

Let the length of the two trains be L (same length).

⇒ 54 = $\frac{L+L}{(40-30)\times {\displaystyle \frac{5}{18}}}$

⇒ 54 × 50/18 = 2L

⇒ 2L = 150

⇒ L = 75 meters

Hence, option (d).