Two charges are located on the $x$ axis: $q_1=+6\mathrm{.}4C$ at $x_1=+4\mathrm{.}8cm,$ and $q_2=+6\mathrm{.}4C$ at $x_2=-4\mathrm{.}8cm.$ Two other charges are located on

the $y$ axis: $q_3=+2\mathrm{.}7C$ at $y_3=+4\mathrm{.}8cm,$ and $q_4=-5\mathrm{.}8C$ at $y_4=+6\mathrm{.}5cm.$ Find $($a$)$ the magnitude and $($b$)$ the direction of the net electric

field at the origin.