If it takes 15 minutes to dry your hair with a 1.200 kw hair drier, how much energy is used in drying your hair?

1.2 kW is 1.2 kJ per second.

15 minutes is 900 seconds.

900*1.2 = 1080 kJ or 1080000 J

The problem here is that according to aufbau principle before 3d orbital 4s subshell comes.after filling 3p orbital with electrons you have 4 electrons left, you place two in 4s with opposite spin and the other two in 3d in any of its two orbitals of total five orbitals with the same spin.