A ladder 10m long is set against a vertical wall, Calculate the height of the wall where the ladder reached a foot of the ladder is 6m away from the wall.

8m

Step-by-step explanation:

You can consider lost yards as negative, and gaines yards as positive. So, if they lost 9 yards and then gained 9 yards, the expression is

-9+9=0

This means that the team is exactly where it started (which maked sense, because they lost exactly as much as they gained.

If they gained first and lost then, it wouldn't change a thing: you'd have

9-9=0

and so the team is always where it started.