Mechanics question?

Take g = 9.8 m/s²
h = ut - (1/2) gt²

For the first stone:
h = (30)(3) - (1/2)(9.8)(3)²
Displacement, h = 45.9 m

For the second stone:
h = (-30)(3) - (1/2)(9.8)(3)²
Displacement, h = -134.1 m

Distance apart of the two stones after 3 seconds
= 45.9 - (-134.1)
= 180 m

The solution becomes still easy if you assume the first stone moving down wards ( instead of upwards) with an initial velocity of (-)ve 30 m/s and g +ve. Herte you wont need to put the value of g since it gets cancelled out.