In the figure what are the $($a$)$ magnitude and $($b$)$ direction $($from $x-$axis in the counterclockwise direction$)$ of the net electrostatic force on particle $4$ due to the other three particles? All four particles are fixed in the xy plane, and $q_1=-54\mathrm{.}40{10}^{-19}C,q_2=+54\mathrm{.}40{10}^{-19}$ C$,q_3=+108\mathrm{.}80{10}^{-19}C,q_4=+54\mathrm{.}40{10}^{-19}C,{}_1=44,d_1=6\mathrm{.}10cm,$ and $d_2=d_3=3\mathrm{.}50cm.$

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$($b$)$ Number

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