Hello,

First of all convert the speed of the train in m/s

So 45 kmph = 12.5 m/s

Now the distance the train would cover in 30 seconds can be found out by using the simple maths ie distance = speed × Time.

so distance covered by train = 12.5× 30 = 375m.

Now the train will cross the bridge completely when It accomplishes the following journey-

"The engine was at the beginning of the bridge and after crossing the bridge the last coach was at the other end of bridge".

Hence we will subtract length of train from total distance.

So the length of the bridge = 375-130 = 245m

Hi

Answer :- the bridge's length  is 245 m

EXPLANATION

We have

Speed= 45 km/ hr

= (45× 18/ 5 )m/sec

= 25/2 m/sec

Now, time = 30 sec.

Let us assume the length of bridge be x.

Then,

Distance/ time = speed

130+x/ 30 = 25/2

Or 2(130+x)=750

Or x=245m

Hence, length of the bridge is 245 m

Thank you