Since the angles of a triangle have to add up to 180 degrees, and angle A is 28 degrees, and angle B is 74 degrees, angle C would have to be 78 degrees so there are a total of 180 degrees in the triangle. Since triangle ABC is similar to triangle DEF, the angle measurements of that triangle would also have to be 28 degrees, 74 degrees, and 78 degrees, corresponding to angles D, E, and F. Since the largest of these numbers is 78 degrees, and angle F is the largest angle of the triangle, that would be your answer.
