Among the complex numbers $z$ which satisfies $|z-25i|\leq 15$, find the complex number $z$ having:
(A) Least positive argument
(B) Greatest positive argument
(C) Least modulus
(D) Greatest modulus
As $|z-25i|\leq 15$ represents the boundary and interior of a disk, I think the maximum and minimum modulus can be found along the line joining centre and origin. But I am not able to think about argument part. What should be the approach in that case?