When translating a triangle, the distances between points do not change. Therefore, if triangle ABC is translated four units to the left to create triangle A'B'C', the length of side A'C' will be the same as the length of side AC.
If you are given the lengths of the sides in triangle ABC (which are not provided in the question), you can use that information to determine the length of A'C'.
Please verify the length of side AC in triangle ABC to compare it with the options provided. If the length of AC is known, that will directly determine the length of A'C'.
If you need further assistance or if you can provide the lengths or any additional details, I can help you deduce the length of A'C'.