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

Wind or electric energy force force of friction

Letter a, because when there are unlike charges they will always attract to each other.