A new oil pump costs $7,000 and has no salvage value once installed. The manufacturer's warranty will pay the 1st year maintenance and repair costs. In the 2nd year, costs will be $900, and they will increase on a $500 arithmetic gradient in subsequent years. Also operating expenses for the pump will be $500 the first year and will increase on a $400 arithmetic gradient in the following years. If interest rate is 8%, compute the pump's equivalent annual cost in its 4th year of operation

(Note: Don't use the $ sign in your answer and keep 2 decimal places)