Instructions: You are given a paragraph, with numbered sentences, and a question. Write the numbers of the sentences needed to answer the given question. Separate multiple sentence numbers with a comma (", "). E.g. "1, 2" would be the correct response if Sent 1 and Sent 2 are needed to answer the given question (do not include sentences that contain no information that is necessary to answer the question). Sort the sentence numbers in an increasing order (i.e., '1, 2', instead of '2, 1'). Your answer should not contain anything than the sentence numbers separated by a comma (e.g. '1, 2, 3, 4'). The given question requires more than one sentence to answer. So, your answer must contain at least one comma (", ").
Input: Paragraph- Sent 1: What happens when two forces act in opposite directions?
Sent 2: Net force is the difference between the two forces.
Sent 3: In other words, one force is subtracted from the other.
Sent 4: Think back to the book example.
Sent 5: One force was opposite the other.
Sent 6: The forces were equal in each direction.
Sent 7: In this case, the net force is zero.
Sent 8: Because the forces on the book are balanced, the book doesn’t move.
Sent 9: It does not fall to the ground.
Sent 10: The table is not breaking.
Sent 11: The book is not falling to the ground.
Sent 12: Both are evidence that the force are balanced.
Sent 13: Situations like these are common.
Sent 14: Can you think of objects sitting on shelves or tables?
Sent 15: These are all examples of balanced forces.
Sent 16: Thanks to balanced forces objects stay where you put them. 
Question: What is it called when you put an object on a shelf or table and it doesn't move?.
Output:

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
user
14, 15.