Normal
\[\begin{cases} & \text{} v_{A}-v_{B}=\frac{S_{x}}{t_{x}} = -30km/h\\ & \text{} v_{A}+v_{B}=\frac{S_{n}}{t_{n}} = 120km/h \end{cases}\Rightarrow \begin{cases}& \text{} v_{A} = 45km/h\\ & \text{} v_{B} = 75km/h \end{cases}\]
