The answer should be A. In order to solve these half-life problems, I encourage you to find an algebra calculator online, and plug in these numbers. The remaining grams goes in front, so 3.
The entire equation should look something like 3 = 15(1/2)^t/4.95
The 4.95 represents how long it takes before the sample halves, t is your answer, 1/2 represents the value halving every 4.95 hours, 15 is the initial sample size, and 3 is the end result that remains.
The overall answer should be about 11.5 hours, as per an algebra calculator.
Hope this helps solve any other similar problems
