Let zinC such that $|z|=5$ with $Re(z)>0.$

$($a$)$ Compute

Arg$(\frac{z+5i}{z-5i})$

and enter its value in the box below.

Syntax advice: Enter your answer using Maple syntax, for example, enter $5$ as $5*$ Pi $.$

$($b$)$ Briefly explain in words, in one or two sentences, how you obtained your answer in part $($a$).$