Time taken by the train to cross a 220 m long tunnel is 30 seconds.

Explanation

• Length of train: l(train) = 280 m
• Length of tunnel: l(tunnel) = 220 m
• Train speed: v = 60 km/hr

To cross that tunnel, because l(tunnel) < l(train), the minimum distance needed is:
d = 2×l(tunnel) + Δl
⇔ d = 2×l(tunnel) + l(train)–l(tunnel)
⇔ d = [ 2×220 + (280–220) ] m
⇔ d = [ 440 + 60 ] m
⇔ d = 500 m = 0.5 km

The minimum time needed:
t = d/v
⇔ t = (0.5 km) / (60 km/hr)
⇔ t = (1/120) hr
⇔ t = (1/120) × 3600 seconds
⇔ t = 30 seconds

CONCLUSION

∴  Time taken by the train to cross a 220 m long tunnel is 30 seconds.