Physics

Two blocks are hung by a string draped over a pulley, a 1.3-kg block on the left and a 3.4-kg block on the right. The two blocks start out at rest and at the same height.

part 1:
What is the change in the gravitational potential energy of the system of blocks and Earth when the 3.4-kg block has dropped 0.47m ? (Maybe this is important, but I just need the answer to part three)
answer is =-9.7J

part 2:
What is the change in the kinetic energy of the system between release and this instant? (Maybe this affects part three)
Answer to this part is 9.7J

part 3:
What is the velocity of the 1.3-kg block at this instant?
need answer