ET 350 3 3/01/2018 4.Maintenance costs for a regenerative thermal oxidizer have been increasing uniformly for 5 years. If the cost in year 1 was $8000 and it increased by $900 per year through year 5, the present worth of the costs at an interest rate of 10% per year is closest to (a) $31.670 (b) $33.520 (c) $34.140 (d) Over $36,000 5. The present worth of an increasing geometric gradient is $23.632. The interest rate is 6% per year, and the rate of change is 4% per year. If the cash flow amount in year 1 is $3000, the year in which the gradient ends is year.... (a) 7 b) 9 (c) 11 (d) 12 6. The time it would take for money to double at a simple interest rate of 8% per year is closest to (a) 10 years (b) 25 years (c) 15 years (d) 20 years