In the context of right triangles, the Hypotenuse-Leg (HL) Theorem states that if two right triangles have equal hypotenuses and one pair of legs that are equal, then the triangles are congruent.
In your problem, you mentioned \( AC = 84 \) m and \( AD = 85 \) m. However, the triangle sides and how they correspond aren't entirely clear without more context or a visual aid.
If we assume that triangles \( ABC \) and \( CDA \) refer to two right triangles where:
- \( AC \) is the hypotenuse,
- \( AD \) is the leg of triangle \( CDA \),
and you want to find the length \( BA \), we need more information about the triangle structure or any additional triangle side lengths.
However, if we use a broader interpretation:
In right triangle \( ABC \):
- if we assume \( AC \) is a leg of triangle \( ABC \) (not the hypotenuse) and suppose \( AB \) is also one of the legs, we need information about the angle at \( A \) or the configuration of points to solve for \( BA \).
Please provide additional information or specify the relationships and configurations of your triangle sides so I can assist further!