Call that vertical & horizontal distance 1.
If you walk along the top of the hill (parallel with the bottom) for a distance x.
The HORIZONTAL distance back to the starting point would be .
You are looking for the horizontal distance, in this case, to be 2.
You have a triangle. Base (adjacent side) of length 1, and the hypotensue of length 2.
The angle you require (from the north direction straight up the hill):