Maintenance costs for a small bridge with an expected 50-year life are estimated to be $1,000 each

Question:

Maintenance costs for a small bridge with an expected 50-year life are estimated to be $1,000 each year for the first 5 years, followed by a $10,000 expenditure in the year 15 and a $10,000 expenditure in the year 30. If i = 10% per year, what is the equivalent uniform annual cost over the entire 50-year period?