The energies of the 3s, 3p and 3d orbitals in a multi-electron atom increase in that order. To which factor(s) can this order be attributed?

(P) The relative penetrations of these orbitals near the nucleus. 

(Q) The relative average distance of the electron from the nucleus.

Here for the energies of the 3s, 3p and 3d orbitals in a multi-electron atom increase in that order. So the order will be,
3 s<3 p<3 d

Consequently, the relative average distance of the electron from the nucleus and the respective penetrations of these orbitals close to the nucleus.