Hi Khushi,

Let us assume that the length of racetrack is x kms.

so, now when A covers x kms then, B covers (x-45)kms and C covers (x-90) kms.

And when B covers x kms,then C covers (x-50) kms.

We have concluded from the given question is that the ratio of speed of racers is same as the ratio of distance covered in a specific given time.

Therefor, Ratio of speed of B and C,

(Speed of B) / (speed of C) = (x - 45) / (x-90) = x / (x-50)

=> x / (x-50) = 45/40

After solving this, we get x = 450 kms.

Hope it helps to clear your dilemma, thankyou!