Using the equation of motion relating distance traveled (s) to initial velocity (u), time (t) and acceleration (a):
s = ut + 1/2 at^2
Here, initial velocity = 0, since the skier was at rest, distance traveled is 75 m and time taken is 15 seconds,
s = 0 + 1/2 a t^2
Or, a = 2s/t^2 = 2 x 75/15^2 = 0.67 m/s^2.
Thus, the skier is accelerating at the rate of 0.67 m/s^2.
Hope this helps.