I need help with question 7.18. I looked at the solution for this questions but it was a given a thumbs down and I don't know why

7.17 Barron Chemical uses a thermoplastic polymer to enhance the appearance of certain RV panels. The initial cost of one process was $130,000 with an- nual costs of $49,000 and revenues of $78,000 in year 1, increasing by $1000 per year. A salvage value of $23,000 was realized when the process was discontinued after 8 years. What rate of return did the company make on the process? Solve by trial and error and verify i* by spreadsheet. 7.18 Steel cable barriers in highway medians are a low- cost way to improve traffic safety without over- stressing department of transportation budgets. Cable barriers cost $44,000 per mile, compared with $72,000 per mile for guardrail and $419,000 per mile for concrete barriers. Furthermore, cable barriers tend to snag tractor-trailer rigs, keeping them from ricocheting back into same-direction traffic. The state of Ohio spent $4.97 million in- stalling 113 miles of cable barriers. Answer the 202 Chapter 7 Mu 7.2 following using both tabulated factors and a spreadsheet function. (a) If the cable barriers prevent accidents totaling $1.3 million per year, what rate of return does this represent over a 10-year study period? (b) What is the rate of return for 113 miles of guardrail if accident prevention is $1.1 million per year over a 10-year study period? 7.19 Aloma, a university graduate who started a suc- cessful business, wants to start an endowment in her name that will provide scholarships to IE stu- dents. She wants the scholarship to provide $10,000 per year and expects the first one to be awarded on the day she fulfills the endowment obligation. If Aloma plans to donate $100,000, what rate of return must the university realize in order to award the $10,000 per year scholarship