The general formula for the distance between two points is

Anyway, if A and B have the same x or y coordinates, this formula can be simplified. For example, in this case the two points have the same x coordinate of -8, so the following part of the formula simplifies:

So, we're left with

but the square root of a square is the absolute value of the object being squared:

which is this case means 
which is the correct length of the side.
650 kgs is equal to 1,433 lbs. I believe the mistake would be that they forgot to add a period in between 65 and the 0, because 65.0 kgs is equal to 143.3 lbs.