Let 'v' represent the speed of the car.

Assuming that by 'the speed of the train is 5 km greater than the speed of the car' you mean 'the speed of the train is 5 km per hour greater than the speed of the car' follows 'v + 5' represents the speed of the train.

t1 = 4 hr is the time of the car

t2 = 7 hr is the time of train

d = 255 km the total distance traveled

Since distance = speed*time we have:

vt1 + (v + 5)t2 = d

4v + 7(v + 5) = 255

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click here to see the equation solved for v

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v = 20 km/hr

v + 5 = 20 + 5 = 25 km/hr

The speed of the train is 25 km/hr.