We can find out what LM is based on the fact that the bases of the 2 triangles are the same, this would also mean that the hypotenuse sides of the triangles should also be the same as well. Thus the sides of LM should also equal the sides of MN.
Another way, is to assume that the triangles are right angle ones, and use Pythagorean theorem to solve for the height and use that to solve for the hypotenuse.
