I am lost. Please help me solve this. I know it will be simple if I can just see it. Thanx.

A sample of 500g of radioactive lead 210 decays to polonium 210 acording to the function defined by A(t)= 500e^-.32t,t is for time in years. find the amount of the sample remaining after 4 years. There is more but I think I can find it if I have this part. Thanx