Answer:
y = x - 5 + 5
Let x be the the original position and y be the new position.
After rid down, 5 floors, the expression would be y = x - 5.
After rid back up 5 floors, the expression changed to y = x - 5 + 5.
Hence, the required expression is y = x - 5 + 5 = x.
Explanation: