You can
put this solution on YOUR website!I think you meant to say 1 meter of cable is to be used for tying. At least I hope so, because I don't know how long 1, is.
1 meter down from the top of the pole makes one side of the triangle 5 meters. Using 1 meter of the 6.5 meter cable for tying leaves 5.5 meters for the hypotenuse of the triangle.
Pythagoras says:

where

and

meters