Answer:
They are similar because of the SAS triangle similarity theorem.
Explanation:
The angles in the interconnection of the two triangles are the same because they have the same vertex and lines.
The two sides are similar by a ratio of 1.5.
9/6 and 6/4 both equal to 1.5, which means that they have the same ratio.
Because there is a side that's similar, an angle that's congruent, and then a side that's similar, you can say that the triangles are similar basing on the SIDE-ANGLE-SIDE triangle similarity theorem.