The triangles are similar.
If we look at the 102-degree angle in the middle, we can subtract it from 180(a straight line) and divide it in half which gives us (180-102)/2=39.
The other two angles in the left triangle(90 and 51), sum up to 180 when added with 39. The other triangle is the same since the interior angles of a triangle are 180 degrees and we know two angles(39 and 90).
We now know that those two triangles have 3 exact angles, so they must be similar.