Answers by visitors named: Dr. Loveday

For the the first part you have it right. For the second part, the momentum equals zero because the momentum before she just is zero. After she jumps, the make the total momentum zero, the momentum of the raft and the momentum of the girl must be equal in size but opposite in direction. For the third part is the same. 0= (Mass of girl)*(velocity of girl) + (Mass of raft)*(velocity of raft)