The triangles PRQ and MRN has a congruent angle, the angle in vertex R is a common angle, a right angle (angle of 90°): 1) Angle PRQ of triangle PRQ is congruent with angle MRN of triangle MRN
The sides that form the congruent angle in triangle PRQ has a proportion of: (Major side) / (Minor side) = RQ / PR = 18 / 12 = 1.500
The sides that form the congruent angle in triangle MRN has a proportion of: (Major side) / (Minor side) = MR / RN = 8 / 6 = 1.333
2) The side that form the congruent angle are not proportionals (1.500 in triangle PRQ and 1.333 in triangle MRN).