#51. Challenging Maths Question

Contributed by my student. (: I had a good time solving it. Thank Wyatt!

Yesterday night, BaiKah decided to go for a walk on the railway bridge as he thought there will be no trains in operation at that point of time. However, he was wrong! When he was halfway across the bridge, he saw a train 160m away (the train may or may not reach the railway bridge yet). Due to the injury on his leg, he could only turn back and walk at the same speed as he was walking just a moment ago. Fortunately, when he just reached the end of the bridge and hopped off the track, the train went past at that very moment. If he had attempted to walk to the other end of the bridge, the train would have struck him 4m before the end of the bridge.

Question: How long is the bridge?