8. If the present value of a perpetuity is $6,000 and the discount rate is 8%, what is the amount of the payments? 9. At an 8% rate of interest, how long does it take for a sum of money to double? 10. What is the rate of return on an investment if you lend $1,000 and two years later are repaid $1,254.70 ? 11. What is the rate of interest on a $10,000 loan that is to be repaid in 10 equal annual installments of $1,917 each