\(\lambda_{\text {obs }}=670.7 \; nm\)
\(v =?\)
\(c =3 \times 10^{8} \; m / s\)
If \(v << c\)
\(\frac{\lambda_{\text {obs }}-\lambda_{\text {emitted }}}{\lambda_{\text {emiited }}}=\frac{ v }{ c }\)
\(\frac{670.7-670}{670}=\frac{ v }{ c }\)
\(V =3.13 \times 10^{5} \; m / s\)