The car covered the first part of the journey (30 km) at a speed of 15 m / s

The car covered the first part of the journey (30 km) at a speed of 15 m / s, and the second part (40 km) in 1 hour. What was the average speed of the car along the way?

S1 = 30 km = 30,000 m.
V1 = 15 m / s.
S2 = 40 km = 40,000 m.
t2 = 1 h = 3600 s.
Vav -?
In order to find the average speed of movement Vav, you need to divide the entire distance S traveled by the entire time of movement t: Vav = S / t.
S = S1 + S2.
t = t1 + t2.
For uniform movement, the movement time is determined by the formula: t1 = S1 / V1.
Vav = (S1 + S2) / (S1 / V1 + t2).
Vav = (30,000 m + 40,000 m) / (30,000 m / 15 m / s + 3600 s) = 12.5 m / s.
Answer: the average vehicle speed Vav = 12.5 m / s.