how do orbital energies change from one subshell to the next

Solution

Energy of a subshell (orbital) is determined by (n+l) value where n is principal quantum number and l is azimuthal quantum number.

Orbitals are filled based on (n+l) value.

The subshell with lowest (n+l) value will be occupied first and later the higher (n+l) value.

If subshells have same (n+l) value then orbitals are filled based on n value.

The subshell or orbital having lowest n value will have lower energy.