For this chain-of-thought reasoning and answer, what was the question?
Since a dozen has 12 eggs, the total number of eggs that Addilynn bought is 6 dozen * 12 eggs / dozen = 72 eggs. If she used half of the eggs, the number of eggs left is 72 eggs / 2 = 36 eggs. While moving the eggs to clean the shelves, she broke 15 eggs, leaving 36 eggs - 15 eggs = 21 eggs.
 A: 21
Q: Addilynn went to the grocery store and bought six dozen eggs for use in her house. After two weeks, she used half of the eggs, then accidentally broke 15 of the remaining eggs while moving them to clean the shelves. How many eggs are left on the shelf?