$$ \put \begin{cases} s:\text{ship}\\g:\text{gas}\\\end{cases} $$$$\put \dot y=\dyt{y},$$$$ \begin{cases} v_i&=6.0\times10^3\ut{m/s}\\v_{g\larr s}&=-3.0\times10^3\ut{m/s}\\m_s&=2.5\times10^4\ut{kg}\\a_s&=2.0\ut{m/s^2}\\M&=m_s+m_g\\\end{cases} $$$$\Delta \Sigma \vec p=0,$$$$ \begin{cases} Mv_i&=m_gv_{g}+m_sv_s\\v_{g\larr s}&=v_g-v_s\\\Delta v_s&=v_s-v_i\end{cases} $$$$ \begin{aligned}-m_gv_{g\lar..