i will answer Q:1 for u and give u hints for other two questions.
Question 1
Average Speed = Distance / Time = 24 / 0.5 = 48 m/s
Question 2
for part a)
when any object reaches its maximum hieght then the velocity is zero.
for part b )
as i told you before that average speed is equal to the distance travelled divided by the time taken.
part c )
use the free fall equation to find out the hieght of the building.
Question 3
for part a ) to find the net force you have to know all the forces that are acting on the box , you have the horizontal force given , you have the frictional force that is directed to the opposite direction of box's movement and finally you have the wight of the box directed downwards .
add up all these forces together to get the net force.
part b ) you found it in part a right check it.