This is the 1/2 life formula. At time 0, the sample starts out 288 mg. That's the peek amount as far as he is concerned. It doesn't matter how that 288 mg got there. It only matters that that is his starting point. An hour later, he has 144 mg left. 2 hours later the number dropped to 72 and so on down.
So here are your answers
If you are curious
Formula: P = A(1/2)^(x) where x starts at 0.