To determine the length of side \( a \) based on the information you've provided, we need to follow the AAS (Angle-Angle-Side) Congruence Theorem. This theorem states that if two triangles have two pairs of angles and the side between those angles congruent, then the triangles are congruent.
Since you've indicated that the triangles are congruent by the AAS Congruence Theorem, this means that \( a \) must be equal to the corresponding side of the other triangle.
Since I don't have the specific numerical values or details about the triangle in the image you reference, I cannot give the exact value of \( a \). However, you should determine the corresponding side length in the left triangle that corresponds to \( a \) and that will be the length of side \( a \).
If the left triangle's side that corresponds to \( a \) is \( x \), then:
Side \( a \) must be \( x \).
Make sure to check the triangle's numerical values you have in the image to find the specific length!