1) "Solve the equation: The price of a new car is $28,000 and it depreciates 9% each year. How much is the car worth in 6 years?"

I THINK #1 is as follows...

y = 28,000(1+/-0.09)^6

y = 28,000(+/-1.09)^6

y = 28,000(1.678)

y = 46,984

And this looks completely wrong to me.

2) "Solve the equation: A population of 175 snails is increasing at an annual rate of 12%. At this rate, how long will it take for the population of snails to reach 315?"

I have absolutely no idea.

I know that I should apply the formulas y = ae^+/-kt and y = a(1+/-r)^t, but I'm not quite sure for which type of problem uses which formula. I do believe that y = a(1+/-r)^t is used for money, but again, I'm just stuck on how to do these. Thanks in advance to anyone who'll tackle these.