only part i cant get correct is C.

A new computer system will require an initial outlay of $18,750, but it will increase the firm's cash flows by $4,200 a year for each of the next 6 years. a. Calculate the NPV and decide if the system is worth installing if the required rate of return is 8%. Note: Negative amount should be indicated by a minus sign. Do not round intermediate calculations. Round your answers to 2 decimal places. b. Calculate the NPV and decide if the system is worth installing if the required rate of return is 13%. Note: Negative amount should be indicated by a minus sign. Do not round intermediate calculations. Round your answers to 2 decimal places. b. Calculate the NPV and decide if the system is worth installing if the required rate of return is 13%. Note: Negative amount should be indicated by a minus sign. Do not round intermediate calculations. Round your ans 2 decimal places. c. How high can the discount rate be before you would reject the project? Note: Do not round intermediate calculations. Enter your answer as a percent rounded to 2 decimal places