Three point charges are located on a circular arc as shown in the figure below. $($Let r $=4\mathrm{.}40$ cm$.$ Assume that the $+$x$-$axis is to the right and the $+$y$-$axis is up along the page.$)($a$)$ What is the total electric field at P$,$ the center of the arc? $($b$)$ Find the electric force that would be exerted on a

$4\mathrm{.}94$ nC point charge placed at P$.$