The question can be solved using conservation of linear momentum.
[tex]M_{a}[/tex] = 0.06kg and [tex]M_{b}[/tex] = 0.03kg
Let the initial velocity of Marble A be , [tex]V_{a1}[/tex] = 0.7m/s
Let the initial velocity of Marble B be, [tex]V_{b1}[/tex] = 0m/s
Let the velocity of Marble A after collisiong , [tex]V_{a2}[/tex]= -0,02m/s
Let the velocity of Marble B after collision be [tex]V_{b2}[/tex]
From the conservation of linear momentum equation. We get,
[tex]M_{a}V_{a1}+M_{b}V_{b1}=M_{a}V_{a2}+M_{b}V_{b2}[/tex]
Substituting the values we get,
(0.06)(0.7) + 0 = (0.06)(-0.02) + (0.03)[tex]V_{b2}[/tex]
we get, [tex]V_{b2}[/tex] = 1.44m/s