Applications of exponential equations

I have two problems on my test review that I have no idea where to start.

1.) The population of Merchantville was 20,000 in 1990 and 25,000 in 1995. If exponential growth is assumed, find a model for the population growth and then use the model to determine the population in 2008.

2.) A sample of 500 grams of radioactive lead 210 decays to polonium 210 according to the function A(t)=500e^-.032(t), where t is in years. Find the amount of the sample remaining after half-life.

Thanks in advance!