assignment: goat tethered to the corner of rectangular shed

a goat is tethered to a corner of a 4m by 5m shed by 6m rope what is the maximum area the goat cover?

The problem did not mention if the goat can go inside the shed or only allowed outside the shed. The following figure assumes that the goat don't have any access inside the 4m by 5m rectangle.
 

plane_003-goat-tethered-rectangle.gif

 

What is your answer?