Astudent says that if two sides and one angle of one triangle are congruent to any two sides and one angle of another triangle, then the two triangles are congruent. what mistake did the student make?

The student made the following mistake: The student said that two sides are congruent to any two sides of another triangle and this is not correct.
 The explanation is shown below:
 By the SAS Theorem (Side, Angle, Side), two triangles are congruent when two sides and one angle of one of the trianglesare equal to the corresponding sides and one angle of the other triangle. Therefore, as you can see, the sides must be corresponding.
 

It would be 18 cm