To analyze Sebastian's movement, he first goes up 7 floors (which we can represent as +7) and then goes down 9 floors (which we can represent as -9).
This means he can express his total movement starting from a neutral position (0) like this:
- Starting from 0, going up 7 floors can be represented as: 0 + 7
- Then, moving down 9 floors from there can be represented as: (0 + 7) - 9 or simply 7 - 9.
If we look at Sebastian's expression of 9 + (-7), it doesn't correctly represent his movements as it suggests starting from 9 floors rather than from a neutral position.
Among the responses provided, the most appropriate one is:
Sebastian should have used –9 and 7.
Because moving down 9 floors can be represented as -9 and moving up 7 floors can be represented as +7. Thus, he should consider his position more correctly reflecting the down movement first.