Stuart tethered his goat to one end of a $20$-foot length of rope and attached the other end of the rope to a hook fixed to the side of his shed.

When he came back the goat had eaten all the grass within its reach.
Here is a picture showing the region eaten by the goat:

 

Where did Stuart fix the rope?

What was the area available to the goat?

Could the goat have eaten more grass if the rope had been attached to a different point on the shed?