QA train passes two people who are walking along a railway track. The first individual walks at 4.5 kilometres per hour, whereas the second walks at 5.4 kilometres per hour. Overtaking them takes 8.4 and 8.5 seconds, respectively. What is the train's speed if both people are walking in the same direction as the train?

In this problem, we are given the lengths of two trains and the time it takes for them to pass each other. From this information, we want to find the speed of the trains.

To do this, we can use the formula for speed, which is distance traveled divided by time taken. We can set up two equations, one for each train, using this formula.

The first equation will be for the first train, and will look like this: x/t1 = (y-z) (10/36), 

where x is the length of the train in meters, t1 is the time it takes for the train to pass, y is the speed of the first train, and z is the speed of the second train.

The second equation will be for the second train, and will look like this: x/t2 = (z-y) (10/36), 

where x is the length of the train in meters, t2 is the time it takes for the train to pass, y is the speed of the first train, and z is the speed of the second train.

We can then solve these equations simultaneously by dividing one equation by the other. This will give us an equation that contains only y, which is the speed of the first train. We can then solve for y to find the speed of the first train.

In this particular problem, 

we are given that x/8.4 = (y-4.5)(10/36) for the first train 

x/8.5 = (z-5.4)(10/36) for the second train. 

We can then divide these two equations to get 8.5/8.4 = (y-4.5)/(z-5.4). 

We can then rearrange this equation to solve for y, which gives us y = 81 km/hr.