clear & detailed please

6. a) In return for an initial payment of (2a) and a further payment of (a) two years later, an investment guarantees a repayment of (4a) after four years (from the date of the initial payment). Calculate the annual effective rate of interest achieved on this investment. [2 marks] b) A fixed interest security with annual coupon (income) of $7.50 paid annually in arrears will be redeemed at $120 at the end of its term. Given a purchase price of $100 and a required (effective) rate of return of 9% per annum, calculate the maximum term of the security. [3 marks] c) A saver is investing 150 per month from today, in return for a payment of 50,000 in exactly 20 years. Estimate the effective annual rate of return the saver will achieve. [5 marks] [Total: 10 marks]