A negatively charged point particle is moving with velocity vec$($v$)=(4(($km$))/(($s$)))$hat$($z$)$ through a vacuum in the presence of the following external electric and

magnetic fields:

vec$($E$)=(-200($N$)/($C$))$hat$(\backslash$phi $)$ and vec$($B$)=(0\mathrm{.}05($Ns$)/($Cm$))$hat$(\backslash$rho $)$

What is the external electric field observed in a reference frame in which the point particle is stationary?