There are different ways you can divide the area using rectangles and circles. One way is to find the area of the entire width and length, then subtract the empty areas in the corners.
If we take the empty areas and put them together, we find their area is the area of a square minus the area of a circle.
Because the hiker walked directly west and then directly north the two legs of the hike forms a right triangle. Therefore we can use the Pythagorean Theorem to solve this problem.
c=5
The hiker is 5km from camp and should head in a generally south-east direction