\frac{\lambda_1 - \lambda_0}{\lambda_0}= \frac{V_A-V \cos b_a}{c} (1)

\frac{\lambda_2 - \lambda_0}{\lambda_0}= \frac{V_A+V \cos b_a}{c} (2)

(1)+(2) \Longrightarrow V_A=\frac{c}{2 \lambda_0} [ (\lambda_1 - \lambda_0) + (\lambda_2 - \lambda_0) ]

(2)-(1) \Longrightarrow V=\frac{c}{2 \lambda_0 \cos b_a} [ (\lambda_2 - \lambda_0) - (\lambda_1 - \lambda_0) ]

V_A=-2.69 km.s^{-1}

V=29.73 km.s^{-1}