I'm practicing for the CSWP exam and I cannot get the correct mass for question 2 of segment 1.

I have tried two different modeling methods; 1 without equations and 1 with equations, but neither give the correct answer (16490.45 according to the practice exam).

I am getting the correct mass for question 1, using the equations method.

I have double checked the equation values which change for question 2, but still cannot find the error.

Screen shots attached show values for question 1 and 2.

Any help is greatly appreciated.

I glanced at your equations, and saw that you're subtracting 7.5 from "C"....why?