If there were no air resistance, how long would it take a free-falling skydiver to fall from a plane at 3500 m to an altitude of 400 m , where she will pull her ripcord?

By equation of motion we have S = ut + 0.5 a

Where u = Initail velocity, S= dispalcement, t = time taken, a = acceleration

Here S = 3500-400 = 3100m, u = 0m/s, g = 9.8 m/

So, 3100 = 0+0.5*9.8*

        = 3100/4.9

       t =

      t = 25.15 seconds

there are no contact forces mentioned on the list of choices that you've provided.