What is the average speed of a car along the entire path, if it first drove 90 km in 1.5 hours

What is the average speed of a car along the entire path, if it first drove 90 km in 1.5 hours, and then another 60 km at a speed of 120 km / h.

Given:
S1 = 90 kilometers – the first section of the route;
t1 = 1.5 hours – the period of time during which the car drove the first section of the route;
S2 = 60 kilometers – the second section of the route;
v2 = 120 km / h – vehicle speed on the second leg.
It is required to determine the average speed of movement along the entire path vav (km / h).
vav = S total / t total = (S1 + S2) / (t1 + t2) = (S1 + S2) / (t1 + S2 / v2) = (90 + 60) / (1.5 + 60/120) = 150 / (1.5 + 0.5) = 150/2 = 75 km / h.
Answer: the average speed of the car along the entire journey is 75 kilometers per hour.