Marisela make payments into a fund at the end of each month for six years. For the first two years, her monthly payments are $300. For the next two years her monthly payments are $200. For the final two years, her payments are $100. At the end of 12 years, the value of the fund is 20,000. The annual effective interest rate is j and the monthly effective interest rate is k. write an equation of value for time 12 years.