please save question6 and 8. thankyou

Problem 6: Find the present value of an infinite stream of annual payments where the first payment is made att-3, the first payment is equal to $1000, and each subsequent payment is 4% less than the previous payment. The interest rate is 10%. Problem 7: Find the PV of a perpetuity that pays $1000 each 4th year starting at t=1 (i.e., at t=1, 5,9,13, ...). The annual interest rate is 6%. Problem 8: You want to retire in 40 years and you would like to save $1,000,000 by the time you retire. To do so, you plan to set aside a fixed amount of money $C each year for 40 years starting next year. If the annual interest rate is 6%, find C