please help solve exercise 6,7

using Theory of interests formula (explain please)

6.-/1 points Megan wants to buy a car in 4 years for $24,000. She deposits X at the beginning of each month for four years into an account earning 6% compounded monthly. Calculate X. Answer = $ 1 (round your answer to 2 decimal places.) 7.-/1 points Kathy wants to accumulate a sum of money at the end of 11 years to buy a house. In order to accomplish this goal, she can deposit $82 per month at the beginning of each month for the next 11 years or $83 per month at the end of the month for the next 11 years. Calculate the annual effective rate of interest earned by Kathy. Answer = % (in percents rounded to 2 decimal places.)