11. The half life of Potassium (K) to Lead (Pb) is 2 billion years. If a rock is taken to the lab and it is found that it is 6 billion years old, how many half-lives have passed?

11b. If it is found that 2 half-lives have passed how old is the rock?

11c. If the h-l passed has been 4, how old is the rock?

11d. If the rock is 2 billion years old how many h-l have passed?