\(d=\frac{m \lambda_2}{2}=\frac{(m+1)\lambda_1}{2}\)

\(m \lambda_2=(m+1)\lambda_1\)

\(m(\lambda_2-\lambda_1)=\lambda_1\)

\(\frac{2d}{\lambda}\Delta \lambda=\lambda\)

\(d=\frac{\lambda^2}{2\Delta \lambda}=\frac{(490*10^{-9}m)^2}{2(0.0055*10^{-9}m)}=0.218m\)