An electron with a velocity v$=5\mathrm{.}5106$i$^$m$/$s enters a region in which the electric field is E$=450$j$^$V$/$m$.$

a$)$ What is the magnetic field required for the electron not to be deflected?

B$=(0$i$^+0$j$^+8\mathrm{.}18105$k$^)$T

b$)$ If the electric field is switched off, what is the radius of the path in the magnetic field?

$38\mathrm{.}3$cm