I had the same question. I'm pretty sure it's 23 seconds. :)
Explanation:
It is given that,
Mass of Madeleine, 
Initial speed of Madeleine,
(due east)
Final speed of Madeleine,
(due west)
Mass of Buffy, 
Final speed of Buffy,
(due east)
Let
is the Buffy's velocity just before the collision. Using the conservation of linear momentum as :



So, the initial speed of the Buffy just before the collision is 7.13 m/s and it is moving due west. Hence, this is the required solution.
Explanation:
c) is equal to the momentum of the fired bullet
Matter is a thing. ex: paper. notice how paper can be written on. notice how it is ...well, THERE. now notice light. the light is not atoms. it is electricity that does weird stuff to create a big enough source of energy to be a source of light. sorta like fireflies