Final answer:
Before the Missouri Compromise, there were eleven free states and ten slave states in the United States. After the Missouri Compromise, the balance between free and slave states was maintained with the admission of one free state, Maine, and one slave state, Missouri.
Step-by-step explanation:
In 1820, before the Missouri Compromise, there were eleven free states and ten slave states in the United States. After the Missouri Compromise, Missouri was admitted as a slave state and Maine was admitted as a free state, maintaining the balance between free and slave states. Additionally, a line was drawn across the remaining Louisiana Territory, prohibiting slavery north of that line.