Angle AFC is a right angle so it measures 90 degrees. Angle CFB is 42 degrees which is given so angle AFC has to measure 48 degrees because when combined you get 90 degrees. Since AFC measures 48 degrees it is an acute. Again CFB is 42 degrees and CFD is a right angle which is 90 degrees. Angle DFB is the sum total of the two angles so angle DFB would measure 132 degrees which makes it an obtuse angle. CFD is a right so it is 90 degrees because all right angles measure 90 degrees.