The block accelerates down the 30 degree incline at 3m/s2. What is the coefficient of friction of these surfaces

Fnet = Fg sin 30 - Ff

ma = mg sin 30 - mew Fg cos 30

ma = mg sin 30 - mew mg cos 30

a = g sin 30 - mew gcos30

a - g sin 30 = - mew g cos 30

mew = - (a - g sin30) / (g cos 30)

mew = - (3m/s2 - 9.81sin30) / (9.81 cos 30)

mew = 0.22