To get how much a HALF-life is, divide the amount by two getting one half of the original amount. That represents on half-life. so 224= 56 x 4
remember the half-life is fifty-six, so there would be 4 half-lives within 224 seconds. Divide 896 by 2 (448) then again divide by 2 (224) divide by 2 again (112) and again divide by 2 and you would get 56 grams.