In order to identify if the triangles are similar, you first take into account the rect angle of the triangles. Form there you can notice that side ON in the bigger triangle, is similar to the side as RQ in the little one.
So, you calulate the proportion between sides ON and RQ, just as follow:
![(ON)/(RQ)=\frac{8cm}{4\operatorname{cm}}=2]()
Then, the proportion of those sides is 2. This proportion must be the same for the other similar sides of both traingles, in order to conclude that the triangle are similar.
![(PN)/(QS)=\frac{14\operatorname{cm}}{7\operatorname{cm}}=2]()
![(PO)/(RS)=\frac{12\operatorname{cm}}{6\operatorname{cm}}=2]()
Hence, the triangles are similar