A substance undergoes radioactive decay. If you start with 3 grams, after 4 seconds you will have 1 gram left.

a) How long will it take to have 2 grams left?

b) How much will you have after 6 seconds?

c) What is the half-life of the substance?

I have asked about these problems on this site multiple times and I am still very confused on how to do these decay and growth problems (Headbang), any help would be appreciated