There is a formula that you use which is A(t)= P * e^rt. Let me explain. In your problem the P is the principal which is the initial amount you start with. That is 1200. You multiply that by the blue e on your calculator. You press 2nd and then the (e) which is the LN key. The r in the equation is the rate of interest which is 7.3 percent or .073. The t is the number of years that it is in the bank and that is 15. When you multiply the equation you will end up with A(t) which is the amount you will have in the bank after 15 years.
So take 1200*e^(.073)(15)=$3587.02
If calculator is not allowed, you would take your initial amount of 1200(.073) =87.60 and then add this to the $1200 to equal $1287.60. This is your amount after first year. Then you would do this 15 times to get the amount made after 15 years. Second year: $1287.60(.073)=$93.99. Add this to $1287.60 to get $1381.59 for second year.
I don't believe the second step is how they would want you to do this. The calculator way is much more accurate. Sorry for the book!