A 150m long train is moving with a uniform velocity of 45 km/h. The time taken by the train to cross a bridge of length 850 meters is  

Total distance to be covered for crossing the bridge  = length of train + length of bridge $=150\mathrm{m}+850\mathrm{m}=1000\mathrm{m}$
$\mathrm{Time}=\frac{ \mathrm{Distance} }{\mathrm{Velocity}}=\frac{1000}{45\times \frac{5}{18}}=80\sec$