We know angles 3 and 4 = 123°. We also know that they are both located on a straight line, which is 180°. If we subtract 123 from 180, we get 57°, which is the size of the two angles in the smaller triangle KTL is located in.
Now, if we add up all the angles of a triangle, we get 180. With that knowledge, we can subtract 114° (57 x 2) from 180 and get out answer, which is 66°.