Please respond I have this last question and then I can be done this course

Using absolute dating,a fossil is dated to be 3million years old and decomposed 1half-life. If it takes the same fossil 12million years to decompose to 4half-lives, how old will it be when it is measured to be at 3half-lives?

each half life is one half decomposed.

3 million years: one gone
6 million years: two gone
9 million years: three half lives past
12 million years: 4 half lives past

Your teacher is just too easy.