Movement in this problem can be thought as addition or subtraction. Going up a floor means taking your current floor and adding one. Same with going to a lower floor but with subtraction.
The first movement is going down the flight of stairs to reach the 2nd floor - 3.
Why are we using subtraction? Because we are going to a lower level.
2nd floor - 3 = -1 floor or some might consider this the basement.
Now, the next movement is going up 7 floors. This is going to be easy since we know what to do.
