A patient takes a pill that holds 50 mg of medicine in it. The pill is metabolized (reduced or used up) at a rate of 55% every hour. To the nearest thousandth;

a) the amount of the pill that is left after two hours is

b) the amount of the pill that is used by the body after two hours is

I'm having trouble with this question. It pretains to geometric sequences, and I thought I knew how to do these types of "reduction" questions involving precentages but I got the wrong answer on my assignment. Please be thorough in any explanations.