I would assume that the angle of f equals 50°... sincesince the triangles are similar that means that the angles are most likely equal to each other. since the big triangle you can do it 90 + 40 which equals 130 then 180, since that is the total degrees in a triangle, minus 130 equals 50 this means 50 ° is the angle of c. keep in mind angle c equals angle f.
