A) From the horizontal motion it should be evident that the ball reaches the net when t = 0.5 s.

Motion in vertical direction:

a = -9.8 m/s^2

s = 0 m

t = 0.5 s

u = ?

Substitute the data into and solve for u.

B)Motion in vertical direction:

a = -9.8 m/s^2

s = -1 m

u = substitute answer from A)

t = ?

Substitute the data into and solve for t.

Motion in horizontal direction:

u = 24 m/s

a = 0 m/s^2

t = substitute from above.

s = ?

Substitute the data into and solve for s.

Then the answer is s - 12.