What was the exact wording of the problem, including any indication of how many marks were available, and any preamble for the entire test? Was the entire test about triangles?

If you give a congruency statement, such as $\small\triangle \text{ABC} \cong \triangle \text{CHA}$ (ASA), give the letters representing the vertices in the appropriate order (for example, don't state that triangles ABC, AHC are congruent).

If you are writing a detailed proof of congruency, state your assumptions and then choose your approach. A valid approach depends to some extent on how you have been taught to set out a geometrical proof.