I'm sorry to bring up this old thread again, but I'm having the exact same problem. However, I decomposed friction into horizontal and vertical components.
I ended up with these equations:
X: Nsin(A) + fsin(A) = mV^2/R
Y: Ncos(A) - fcos(A) = mg
After dividing I get:
(N+f)/(N-f) tan(A) = V^2/Rg
= N(1 + u)/N(1-u) tan(A) = V^2/Rg
= (1 + u)/(1-u) = V^2/Rg
After solving this for the coefficient (u), I get ~ 0.38. However, the answer is supposed to be 0.34.
g = 9.8
A = 18.785
V = 30