The relative speed of a train in respect of a car is 90

The relative speed of a train in respect of a car is 90 km/h when train and car are moving opposite to each other. Find the actual speed of train . If car is moving with a speed of 15 km/h. ?

Relative speed of train
= Speed of train + Speed of car
⇒ 90 = Speed of train + 15
∴ Speed of train = 90 - 15 = 75 km/h