Please explain the calculation procedure of this problem. (I don't want Excel sheets! I want to know how to calculate this problem

6. Find the present value of an income stream which has a negative flow of $4.500 today, a constant cash flow of $600 per year for years 1 through 8 , a constant cash flow of $800 per year for years' 9 through 20 , and a cash flow of 500 constant cash flow of $800 per year for ascourist rate to be 7.25 percent. NP(7,25,4500,{600,800,500},{8,12,1}