The way that I always solved these problems is just plugging in the values into the given function in the answers. You could also graph these equations, too, and see if the points you've been given are on the graph. I see you're on a Mac, so you should have Grapher on there. Just make sure that if you're using Grapher, you set each equation to y instead of tₓ, since the program won't know what to do with the latter.
For your first problem, whichever function is equal to 17 when you input 1 (since it's the first number in the sequence) for n will be your answer.
87.5 because if your earning a 3.5% of the $500 then that means you're earning 17.5 dollars.in an year therefore in five years you multiply the 17.5 x 5 years which will give you at 87.5 so we've had in total you can get to 587.5 dollars
