Rotate Tom‘s claim around the corner so that the sides of both claims are parallel to each other. Now it is clear that Tom's claim overlaps a quarter of Mike’s claim. This proportion does not vary by rotation because the lost triangle is congruent to the additional triangle. As agreed, Tom gets a share based on half of the overlapping area. Thus, Tom receives half of the quarter (1/8) and gets 12.5 % of the gold find.