We have Vc(t) = Voc + (V(0) – Voc)*exp( - t/Rth*C)
(1)
Here, Rth = 2*4/6 = 4/3 kΩ
And Voc = 4*Vs /(4 + 2) = 4*6/6 = 4 V
V(0) is found at t=0 , here it is V(0) = 8 V
We have Rth*C = 4/3*0.5 = 1/0.67.10-3
Thus we get from eq. (1) Vc(t) = 4 + (8
– 4)*exp( - t/0.67) V , where t is in ms