Here we will use the momentum conservation
Since there is no external force on this system so momentum of woman + canoe system will always remains conserved
So here initial momentum of the system is zero as they are at rest so final momentum will always be zero
[tex]m_1 v_1 + m_2v_2 = 0[/tex]
[tex]57(1.5) + 42(v) = 0[/tex]
[tex]85.5 + 42v = 0[/tex]
[tex]v = -\frac{85.5}{42}[/tex]
[tex]v = - 2.03 m/s[/tex]
so the canoe will go back with speed 2.03 m/s