we know that
[volume of a sphere]=(4/3)*pi*r³
for r= 3 in
calculate the volume of one balloon
balloons=(4/3)*pi*r³-------> (4/3)*pi*3³----------> 113.04 in³
if the rate is 200 in³ --------------------> 1 minute
113.04 in³------------------------> X
X=113.04/200------------> 0.5652
the answer is 0.6 minutes