ANSWER:
10 m/s backward
STEP-BY-STEP EXPLANATION:
We have that for the change of momentum, the following formula:
[tex]m_1\cdot v_{11}+m_2\cdot v_{12}=m_1\cdot v_{12}+m_2\cdot v_{22}[/tex]We substitute, the known values, to calculate the value of Marty's velocity:
[tex]\begin{gathered} 45\cdot-2+90\cdot7=45\cdot-v_{12}+90\cdot1 \\ v_{12}=\frac{45\cdot-2+90\cdot7-90\cdot1}{-45} \\ v_{12}=\frac{-90+630-90}{-45} \\ v_{12}=\frac{450}{-45} \\ v_{12}=-10\text{ m/s} \end{gathered}[/tex]Therefore, Marty's velocity is 10 m/s backward.
