If a solar panel system has an increasing annual maintenance cost (an arithmetic gradient) of $500 per year over an 8 year period, then what is the present value based on 10% interest?

If a solar panel system has an increasing annual maintenance cost (an arithmetic gradient) of $500 per year over an 8 year period THAT STARTS AT YEAR 4, then what is the present value based on 10% interest? To be clear: the total period is 12 years with an 8 year gradient starting in year 4.

If we add an $800 uniform annual payment to the solar panel system of problem #2 (for all 12 years), what is the new total present value? To be clear: this answer depends on a correct answer to problem #2 (where you moved a gradient), which depends on a correct answer to problem #1 (where you calculated a gradient).