Start the clock from when the the stone is projected. Then:
For the lift: x = (5)(3.5) + 3.5 t = 17.5 + 3.5t .... (1)
For the stone: x = -14t + 4.9t^2 .... (2)
Solve equations (1) and (2) simultaneously for x.
Note: I got equation (2) as follows:
Take downwards as the positive direction. Then:
a = 9.8 m/s^2
u = -14 m/s
t = t
x = ?
For checking purposes: