Thank you for your help! I have the answer key but I am not sure what I am doing wrong so please show your work and I will gladly upvote if it is correct!

3. In 1883 the volcano Krakatoa exploded, injecting dust 32 km up into the atmosphere. Fallout from this explosion continued for 15 months. If one assumes that the settling velocity of the particles was constant and neglects slip correction, what was the minimum particle size present at the end of the fallout? Assume that the particles are rock spheres with a density of 2700 kg/m. (15 points)