To get 4% of 800 you times 800 by 4 and divide it by 100. Once you have that amount you add it to 800 to find the amount you will have in your bank the first year.
To get the next year's amount you then get 4% of 832(because after the first year you have more than $800) and then add the 4% to 832, that is the answer for the second year.
To find the third year's amount you get 4% of the new amount (last year's total) and add it to last year's total, that is your total for the third year.
So the first year will be:
(800x4÷100)+800
=32+800
=832
The second year will be:
832+(832x4÷100)
=832+33.28
=865.28
The third year will be:
(865.28×4÷100)+865.28
=34.61(rounded off)+865.28
=899.89
