Question

an object moves from point p to q with an average speed of 60m/s and comes back from point q to p with an average speed of 144km/h . what is the average speed of whole journey in m/s?

Answer 1

The only difficulty here is that they use different unit of speed.
we need 144 km/h to m/s
144 km/h = 144000 m / 3600 seconds
= 400 m/s

let the distance from p to q be x m
time for first leg of trip = x/60 s
time for 2nd leg = x/400 s

avg speed = total distance over total time

so you need to add x/60 + x/400
then divide that into the total distance

I will let you do that, let me know what you got.