Plane Pl1 is the plane containing the three points A 1 6 6 B 2 3 5 and C 2 3 5 Plane Pl2 is the plane containing the three points D 1 1 2 E 4 3 4 and F 2 5 4 Find the smaller dihedral angle in degrees between the planes Pl1 and Pl2 O a 79 O b 26 O c 81 O d 53 28