In order to determine the similarity of the given triangles, verify that the proportion in between similar sides are equal:
PX/AW = 12/16 = 3/4
XM/AL = 15/20 = 3/4
PM/LW = 9/12 = 3/4
as you can notice, the proportions are the same.
Hence, the triangles are similar because of the side-side-side theorem or SSS theorem
