please and a girl out, and if you can explain how you got the answer so i can undertsnad myself

Answer:
9cm
Step-by-step explanation:
If the triangles are similar then their lengths are in a ratio to each other, Ex: PR is 3 times LN, 2*3 = 6cm
This gives us a ratio of 1:3
PQ = LM*3 = 3cm*3 = 9cm