Remark
You would always be wise with this kind of question, to write down your givens and what you want. There is only one formula you can use when you do that.
Givens
vi = 50.0 m/s
vf = 8.0 m/s
a = - 9.8 m/s^2 The negative sign means you are going down whereas the force of the parachute is acting upwards. This is the hard given to get. You have to assume something. What you are assuming is that the acceleration due to gravity remains a constant. I would bet almost anything that thought didn't come up and that makes the question a bit unfair. but there is little else you can assume.
d = ???
Formula
vf^2 = vi^2 + 2ad
Solve
8^2 = 50^2 + 2 * -9.8 * d
64 = 2500 - 19.6 * d Subtract 2500 from both sides
- 2436 = - 19.6 * d Divide by - 19.6
- 2436 / - 19.6 = d
d = 124.2 Answer The person moves 124.2 meters downwards while the parachute is opening
