Find tension and acceleration

(i) Apply: net-force = mass x acceleration to the whole system
(3+5)g.sin(30) - 0.5 = (3+5)a
where g is the acceleration due to gravity (taken as 10 m/s2)
a is the acceleration of the system
hence, a = [8g.sin(30) - 0.5]/8 m/s^2 = 4.94 m/s^2

(ii) Apply: net-force = mass x acceleration to object B again.
5g.sin(30) - T = 5 x 4.94
hence, T = [5g.sin(30) - 5x4.94] N = 0.3 N

what is the purpose of rough and smooth plane?
does friction mean f = 0.5N?