For two triangles to be similar:
-The corresponding sides must be at the same ratio
-The corresponding angles must be congruent
For the triangles ΔLMN and ΔQPN
We know the length of the two sides.
The corresponding sides are:
LN and QN
MN and PN
If the triangles are similar then:
To check if the sides are at the same ratio, you have to calculate the quotient between the corresponding sides:
Both pairs of corresponding sides are at the same ratio.
Now, where both triangles meet, the corresponding angles ∠MNL and ∠PNQ are vertically opposite angles, which means that they are equal.
This means that ΔLMN and ΔQPN are similar by SAS Similarity theorem (first option)