Two trains in opposite directions cross: sum of lengths over sum of speeds

This type of question, asked 2 times: 15 Nov 2020 Tier II, 8 Aug 2022 Tier II. All 2 questions below, oldest first.

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Question 1
15 Nov 2020 Tier II
57 $A train of length 287 m, running at 80 km/h, crosses another train moving in the opposite direction at 37 km/h in 18 seconds. What is the length of the other train?$
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Question 2
8 Aug 2022 Tier II
86 $Two trains whose lengths are 450 metres and 300 metres are moving towards each other at the speed of 162 km/hr and 108 km/hr respectively. If distance between trains is 300 metres, then in how much time, these trains will cross each other?$
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Question 1