Homework problem

When I went through to check this last night it didn't seem to work but I couldn't find my mistake so I asked Khari today but he wasn't sure as well. I was wondering if anyone could help because it's getting pretty frustrating.

116)
a.
p=5000(1-(4/4+e^-0.002x))
600=5000(1-(4/4+e^-0.002x))
600/500=(5000(1-(4/4+e^-0.002x)))
.12=1-(4/4+e^-0.002x)
4/(4+e^-0.002x)=.88
(4+e^-0.002x/1)(4/(4+e^-0.002x)=.88(4+e^-0.002x/1)
4/.88=(.88(4+e^-0.002x/1))/.88
4.5455=4+e^-0.002x/1
.5455=e^-0.002x
ln(.5455)=ln(e)^-0.002x
-.606=-0.002x
-.606/-0.002=-0.002x/-0.002
x=303.026