Answer:
Part a)
The stone which is thrown upwards will lose its speed as it is moving opposite to gravity
Part b)
The speed of stone which is thrown downwards will increase with time as it moves under gravity.
Part c)

so it is less than the half of the total height

Step-by-step explanation:
Part a)
The stone which is thrown upwards will lose its speed as it is moving opposite to gravity
So due to gravitational force the speed of that stone will decrease with time
Part b)
The speed of stone which is thrown downwards will increase with time as it moves under gravity.
The gravitational force on that stone will increase the speed of the stone.
Part c)
the relative speed of two stone is given as

so the time at which two stone will cross the path is given as

now the position at which the two stone cross the path is given as



so it is less than the half of the total height
now plug in the given values
v = 9 m/s
d = 6 m

