The given ratios can be simplified further by doing cross product:

\(\displaystyle{\frac{{{2}}}{{{0.21}}}}={\frac{{{8}}}{{{n}}}}\)

\(\displaystyle{2}{\left({n}\right)}={8}{\left({0.21}\right)}\)

\(\displaystyle{2}{n}={1.68}\)

\(\displaystyle{\frac{{{2}{n}}}{{{2}}}}={\frac{{{1.68}}}{{{2}}}}\)

\(\displaystyle{n}={0.84}\)