A three$-$phase, wye$-$connected $2500$ kVA and $6\mathrm{.}6$ kV generator operates at full$-$load. The per$-$

phase armature resistance Ra and the synchronous reactance, Xa$,$ are $(0\mathrm{.}07+$j$10\mathrm{.}4).$ Calculate the

percent voltage regulation at:

$($a$)0\mathrm{.}8$ power$-$factor lagging, and

$($b$)0\mathrm{.}8$ power$-$factor leading.