is it like this?
in an isolated system, momentum is conserved. so, m1v1=m2v2, were m1 is the mass of boat, v1 is it's velocity, m2 is the mass of all the people, v2 is the velocity of them,
v2=(m1v1)/m2
d2/t=m1/m2 x d1/t
d2=m1/m2 x d1
since every1 covers d1, assume that the center of mass is...