Understanding Half-Life

A half-life is the time it takes for half of a radioactive substance to decay. In this case, every 3 hours, the amount of the substance is cut in half.

Steps to Solve

1. Determine how many half-lives are needed:

* You start with 12g and want to decay to 3g.

* This means you need to reduce the mass by a factor of 4 (12g / 3g = 4).

* Since each half-life reduces the mass by half, you'll need two half-lives (1/2 * 1/2 = 1/4).

2. Calculate the total time:

* Each half-life is 3 hours.

* You need two half-lives.

* Therefore, it will take 3 hours * 2 = 6 hours.

Answer: It would take 6 hours for 12g of the substance to decay to 3g.