A sample taken from a layer of mica in a canyon has 2.10 grams of potassium-40. A test reveals it to be 2.6 billion years old. How much
potassium-40 was in the sample originally if the half-life of potassium-40 is 1.3 billion years?
A. 4.20
B. 8.40 g
c. 12.6 g
D. 16.8 g
E. 25.2 g