\({y}_{1} \text { of red }=\frac{{D} \lambda_{{r}}}{{d}}=3.5\, {mm}\)
\(\lambda_{{T}}=3.5 \times 10^{-3} \frac{{d}}{{D}}\)
Similarly \(\lambda_{{v}}=2 \times 10^{-3} \frac{{d}}{{D}}\)
\(\lambda_{{r}}-\lambda_{{v}}=\left(1.5 \times 10^{-3}\right)\left(\frac{0.3 \times 10^{-3}}{1.5}\right)\)
\(=3 \times 10^{-1}=300\, {nm}\)