There are many approaches. Here is one:

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:

Takedownwards as the positive direction. Then:

a = 9.8 m/s^2

u =-14 m/s

t = t

x = ?

.

For checking purposes:

Spoiler: