mass = 0.25 kg
initial velocity = v_i = 6 m/s
coefficient of kinetic friction = mu_k = 0.1
final velocity = v_f = 0 m/s
distance = d = ?
There are three forces acting on the puck (friction, gravity, normal force) Gravity and normal force cancel each other out, so we can ignore that for now.
Friction acts in the -x direction.
F_n = mg = (0.25 kg)(9.8 m/s^2) = 2.45 N
F_f = (mu_k) * (F_n) = (0.1) * (2.45) = 0.245 N
F = ma ==> a = F/ m = (0.245 N) / (0.25 kg) = 0.98 m/s^2
Finally, we use kinematics.
(v_f)^2 = (v_i)^2 + 2ad
0 = (6^2) + 2(0.98)d
d = 18.367 m
My physics is a bit rusty so this is the best I can come up with.