Petrolyn motor oil is a combination of natural oil and synthetic oil. It contains 2 liters of natural oil for every 3 liters of synthetic oil. In order to make 470 liters of Petrolyn oil, how many liters of synthetic oil are needed

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.