The answer is ASA. Given that ∠A = ∠O, ∠W = ∠N, SW = TN, this shows that the two angles (∠A and ∠W) and the included side SW of the first triangle are equal to the two angles (∠O and ∠N) and the included side TN of the second triangle. This means that third angles ∠S and ∠T are also equal. Therefore, the two triangles ΔWAS and ΔNOT are congruent based from the ASA Postulate.
