Question 8 (10pts) a) A bill of 18,000 dollars falls due on 31 December, 2023. To pay it, the debtor intends to deposit a fixed amount aina savings account at the end of each month. The first deposit will be on 30 September, 2020 and the last on 31 December, 2023. Find at the annual interest rate is 7%, compounded monthly b) A mining company extracts metal ore worth $A of revenue in year O. Its cost per year are SK, a constant. But the company expects its revenue to decline by p each year. It will continue its mining activity as long as its yearly revenue exceeds SK For how many years n' does the company operate? Find the total profit over the period from year to n