Determine the half-life of the substance that decays from A0 to A in time "t".  A0= 51, A= 19, t= 15 hrs

At the beginning of an experiment, a scientist has 256 grams of radioactive goo. After 210 minutes, her sample has decayed to 32 grams. What is the half-life of the goo in minutes? Find a formula for G(t), the amount of goo remaining at time t. G(t) How many grams of goo will remain after 74 minutes?

i have been stuck on this for a while and i am stumped may i have some help please?  Consider a drug that is taken in 50 mg doses daily. Suppose that the first dose is taken when t=0 and that t is measured in hours. A) If the half-life of the drug is 5.5 hours, what fraction of the drug remains in the patient after 24 hours? B) Write a general expression for the amount of the drug in the patient immediately after taking the nth dose of the drug. C ) Write a general expression for the amount of the drug in the patient immediately before taking the nnth dose of the drug (for this we only consider n>1). D) What is the long-term minimum amount of drug in the patient?