Answer:

24 km/hr

Explanation:

Let distance be d

Speed (1) = 20km/h

Time taken = distance / speed

= d/20

Speed (2) = 30km/h

Time = Distance/time

= d/30

Average speed = total distance /total time

=( d+d) /{(d/20)+(d/30)}

= 2d / (d/12)

=24d/ d

= 24