The triangles OMN and OJK are similar by SAS Similarity
How to Identify the Triangle Similarity Postulate?
The three triangle similarity theorems to prove triangles similar are:
Side-Angle-Side, or SAS.
Side-Side-Side, or SSS.
Angle-Angle, or AA.
Now, we are told that the triangles OMN and OJK are similar and as such, we this means that the ratio of their corresponding sides are in equal proportion.
Thus:
(30 + 10)/(3 + 1) = 40/4 = 10
Similarly, for the smaller triangle:
30/3 = 10
Thus, the ratios are equal.
We also see that Angle O is common to both triangles and as such:
The triangles OMN and OJK are similar by SAS Similarity