Question 1087346
Start measuring time when the first stone is dropped from the cliff, it falls under gravity 
{{{d[1]=100-(9.8/2)t^2}}}
{{{d[1]=100-4.9t^2}}}
The second stone starts at {{{t=2}}} with an initial velocity of {{{30}}}, also falling under gravity,.
{{{d[2]=100-30(t-2)-(9.8/2)(t-2)^2}}}
{{{d[2]=100-30(t-2)-4.9(t-2)^2}}}
{{{d[2]=100-30t+60-4.9t^2+19.6t-19.6}}}
{{{d[2]=140.4-10.4t-4.9t^2}}}
So then find {{{t}}} when {{{d[1]=d[2]}}},
{{{100-4.9t^2=140.4-10.4t-4.9t^2}}}
{{{-10.4t=-40.4}}}
{{{t=3.885}}}{{{s}}}
Now that you have the time, plug it into either distance formula and calculate the height from the ground in meters.