Think of a function like a template for numbers. You plug in numbers you know and you get a formula that is structured correctly. An outline is just like this because it is a structure for words.
The answer is 45.6. You multiply the beginning amount to the interest rate to understand how much interest you get. Then multiply that by the amount of years the interest is gathered. 570 * .02 = 11.4 * 4 = $45.6 interest. Add this to 570 for the original amount of 615.6.