I have this problem:

The half-life of radium is 1690 years. How much will be left of 32 grams of radium after 6760 years?

I know to use the formula:

y = Ce^(kx) Where C is the original amount, y is the future amount, k is rate, and x is time. I am having some trouble figuring out what pieces go where. I am thinking the 1690 years is the x, but I'm not so sure of the rest. Also..this is off topic, but is it fine that I am asking a lot (maybe too many in some opinions) questions? I have been strugling with calc 2 since I started it monday. The class is Mon-Fri, 2 hours each day. This is a good way for me to learn..by practicing and finding out what I am doing right/wrong to improve my skills. Thanks everyone.