Let n be a function showing the distance from ground level to stone.
For a stone thrown from a building: 
h1(t)=200−2gt2; 
for a stone thrown from the ground: 
h2(t)=V0t−2gt2=50t−2gt2 
When stones meet: 
h1(t)=h2(t) 
200−2gt2=50t−2gt2; 
t=4 
Answer:4 seconds meeting time of stones
 
                             
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