Give the step-by-step reasoning process and then the final answer. Shelby was having a movie party for her birthday. She and her mom made a dozen bags of buttered popcorn and 10 bags of caramel popcorn. Her brother Alan took 3 bags of buttered popcorn and 1 bag of caramel popcorn for his friends. How many bags of popcorn does Shelby have left for the party?
Shelby and her mom made 12 bags of buttered popcorn + 10 bags of caramel popcorn = 22 bags. Of those 22 bags, her brother took 3 bags of buttered popcorn + 1 bag of caramel popcorn = 4 bags. So now Shelby has 22 bags – 4 bags = 18 bags of popcorn left.
The final answer: 18.