Im having problems with decay and growth.

The problems states:

Radioactive Decay: They half-life of phosphorous-32 is 14 Days, if there are 5 grams presently, when will there be 1 gram left?

Doubling your Money: How much time is required for a $1000 deposit to double at an interest rate of 2.5% compounded annually.

I have no idea what to do. Do I have to find an equation?

Please help. Any help would be greatly appreciated.