ASA stands for angle-side-angle, meaning you need an angle then an adjacent side then another adjacent angle to be congruent to say that these are congruent triangles. Because the semi circles represent congruent angles, they share a side (making them congruent) and both have corresponding right angle measures (making them congruent), you can say that these two triangles are congruent by ASA.
Yes, 13 is correct If you draw the right triangle, the two legs will be 5 and 12. 5 and 12 are parts of a Pythagorean triple. 13 completes the triplet.
