For the first one, you must know that the base angles of an isosceles triangle are equal. That means (for the very first triangle) angle N = angle O. Continue from there.
For the second one, you cannot prove that the two triangles are similar, because you are given no information regarding the sides, and you do not have any information about the other angles in triangle KLM.
For the third one, we see that the two triangles are equilateral, because both of them have equal sides. An equilateral triangle will always be similar to another equilateral triangle, because the angles will always be 60 degrees.