A)
Year 7 (2021): 20,000
Year 8 (2022): 20,000 x 1.045
Year 9 (2023): 20,000 x 1.045 x 1.045
By carrying on this sequence, you can either work each year out manually or using the geometric series formula from the reference sheet. In this case, this would be the easiest way to go. So a is 20,000, r would be 1.045 and n would be 6, then just plug in the numbers and you're good to go.
B) Same process as part A), but you definitely want to be using the formula, as manually calculating 12 years would be impossible. Sub it into the formula using a, r and n.