final answer for question (5): 494 where M=500

question (6): 3743.55

I just need the explanation

5 5. Samia purchases a 5-year arithmetically varying annuity-due whose first monthly payment is m and each subsequent monthly payment decreases by 2. The present value of this annuity using a monthly effective rate of interest of 0.50% is 23,080.32 Calculate the amount of the 4th payment in this annuity. 6 6. Using an annual effective rate of discount of d, the following two annuities have the same present value: (0) A 20-year decreasing annuity-due with annual payments of 20, 19, 18, ..., 1 (ii) A perpetuity-due with annual payments of 8. Using the same annual effective rate of discount of d, calculate the present value of an increasing perpetuity-due whose first annual payment is 10 and each subsequent annual payment increases by 10