All you have to do for this is follow the midpoint formula.
Let me know if the picture is unclear and I'll type it out for you.
Answer:
The sharing cone holds about 9 times more popcorn than the skinny cone.
Step-by-step explanation:
Cone volume:

r is the radius and h is the inches.
Skinny-size cone:
Radius is r, height h. So

Sharing size:
Radius is now 3r. So

How many times more popcorn?

The sharing cone holds about 9 times more popcorn than the skinny cone.