A 62 kg water skier, moving at 14 m/s , lets go of the towline.

Momentum= 868 kgm/s
Impulse= -868 Ns
c.If the water exerts an average force of -275 N on the skier, how long must the force act? 3.16 s
d. How far does she travel during this time?

I'm guessing "this time" mentioned in the question is 3.16 s

Get average acceleration during the 3.16 seconds from

a = 14 m/s / 3.16 s

then d = 14 (3.16) - (1/2)(a) (3.16)^2
or more easily from average speed = 7 m/s
so
7 * 3.16