Two triangles are similar if their only difference is its size.
With this in mind we have to find wich sides are corresponding to each other.
First triangle:
From the arrow we notice that the corresponding sides are:

From the last corresponding side we know that the ratio is

This means that the smaller triangle has dimensions of 2/5 the size of the big triangle.
With this in mind we have:

Second triangle:
The corresponding sides in this case are

In this case the ratio is

Therefore
