The region ∣z−5∣≤3 is a disk centered at (5,0) with radius 3. Maximum positive principal argument from origin occurs at the tangent point from origin to the circle.
sinθ=53, cosθ=54.
The tangent point is the foot of perpendicular from (5,0) to the line 3x−4y=0, giving z=516+512i.
5z−12=4+12i⇒∣5z−12∣2=160
5iz+16=4+16i⇒∣5iz+16∣2=272
345iz+165z−122=34×272160=34×1710=20.