Freshman Calculus [Easy, yet long]

[Oblakastouf]

Homework Statement

http://i.imgur.com/ks0WZ.png

Homework Equations

A lot of them.

The Attempt at a Solution

I've got all the right answers up until part four, where you have to solve for C. -5000 is incorrect. I need help setting up to solve C! Please ^_^.

 

[Oblakastouf]

Bump again...