Maximum number of planar atoms in SF6 is (x) and in PCl5 is (y). Difference between  x and y is equal to

Number of atoms in plane in SF6 = 5 (4 F - atoms at corners of the square and 1 Sulphur - atom).Number of atoms in plane in PCl5 = 4 ( 3 Cl - atoms at the corners of triangle and 1 Phosphorous- atom).x - y = 5 - 4 = 1