You're throwing a party and need to figure out how many balloons a helium tank can fill — but every store sells tanks in different sizes and every balloon comes in a different diameter.

Build a single-page widget where the user:
1. Picks a helium tank size from a small preset list (e.g., 8.9 cu ft, 14.9 cu ft, 50 cu ft).
2. Enters the balloon diameter in inches (e.g., 9", 11", 16").
3. Instantly sees how many balloons that tank can fill, calculated from standard helium volume formulas (volume of a sphere = 4/3 π r³, tank volume divided by balloon volume with a ~10% wastage factor).
4. Can add multiple balloon sizes to a list and see a breakdown of how many of each size the tank can fill before it runs out.

The list of balloon entries should be editable — users can remove entries and the totals update live. The UI should be cheerful and clear, showing results in plain language like "Your 14.9 cu ft tank can fill about 41 × 11-inch balloons."