$\overrightarrow{\mathrm{v}} =\left(2 \times 10^{5} \hat{\mathrm{i}}\right) \mathrm{m} / \mathrm{s} $

$\overrightarrow{\mathrm{B}} =(\hat{\mathrm{i}}-4 \hat{\mathrm{j}}-3 \hat{\mathrm{k}}) \mathrm{T} $

$\overrightarrow{\mathrm{F}} =\mathrm{e}(\overrightarrow{\mathrm{v}} \times \overrightarrow{\mathrm{B}})$

$=\mathrm{e}\left[\left(2 \times 10^{5} \hat{\mathrm{i}}\right) \times(\hat{\mathrm{i}}-4 \hat{\mathrm{j}}-3 \hat{\mathrm{k}})\right] $

$=2 \times 10^{5} \times 1.6 \times 10^{-19}[-4 \hat{\mathrm{k}}+3 \hat{\mathrm{j}}]$

Its magnitude is

$\mathrm{F}=2 \times 10^{5} \times 1.6 \times 10^{-19} \times \sqrt{(-4)^{2}+(3)^{2}}$

${=2 \times 10^{5} \times 1.6 \times 10^{-19} \times 5} $

${=1.6 \times 10^{-13} \mathrm{\,N}}$