Charge q$1=7$ nC is located at the coordinate system origin, while charge q$2=0\mathrm{.}55$ nC is located at $($a$,0),$ where a $=0\mathrm{.}75$ m$.$ The point P has coordinates $($a$,$ b$),$ where b $=0\mathrm{.}25$ m$.$ A third charge q$3=16$ nC will be placed later.

$($a$)$  Find the electric potential VP at point P$,$ in volts. Assume the potential is zero at infinity.

$($b$)$  How much work W$,$ in joules, would you have to do to bring the third charge, q$3,$ from very far away to the point P$?$

$($c$)$  What is the total potential energy U$,$ in joules, of the final configuration of three charges?