Suppose that the local government of Columbus decides to institute a tax on seltzer producers. Before the tax, 30 billion packs of seltzer were sold every year at a price of $11 per pack. After the tax, 24 billion packs of seltzer are sold every year; consumers pay $13 per pack, and producers receive $9 per pack (after paying the tax).
The amount of the tax on a pack of seltzer is \boxed{4} per pack. Of this amount, the burden that falls on consumers is $\boxed{4}$ per pack, and the burden that falls on producers is $\boxed{0}$ per pack.
