We must all look for the fg, fn, Ff, and Fnet to get the acceleration.
1 Fg = 28.6 (-9.81)
= 0280.56 n
2 Fn = 280.56 N
3 Ff = μFn
= 0.750 * 280.56
Ff = 210.425 N
4. Fnet = Fa + Ff
= 302 – 210.42
Fnet = 91.576 N
5. F = ma
91.576 = 28.6a
a = 3.2 m/s