Acar moves uphill at 40 km/h and then back downhill at 60 km/h. what is the average speed for the round trip?

Define
d =  distance (km) traveled in either direction
t₁ = time (hours) to travel uphill
t₂ = time(hours) to tavel downhill

The time to travel uphill is

Similarly, the time to travel downhill is


The total travel time is


The total distance traveled = 2d km

The average speed is


The average speed is 48 km/h

(x) - (y) = (1 + 4i)

(3 + 6i) - (2 + 2i) = (1 + 4i)