College Physics (7th Edition)

a) (1) $-x$ b) $1.04\times10^{-6}T$
a). Magnetic field is towards left i.e. (-x) direction. (1) b). $F=qvB$ or, $B=\frac{F}{qv}=\frac{5\times10^{-19}}{1.6\times10^{-9}\times3\times10^{6}}=1.04\times10^{-6}T$