So after I received help earlier today with two problems, I've been flying through my homework. This is until I reached this problem. I don't even know what this applies to, yet alone know how to figure this out. Could someone lay out an equation or something please.

The half-life of radium is 1690 years. If 60 grams are present now, how much will be present in 2450 years? When solving, round the decay constant,r, to 5 decimal places.