Answer:
the amount present 8 hours ago is Ao = 93.338 g
Explanation:
the radioactive decay is given by
A = Ao * 2^(- t/T)
where T = half-life of the substance , t= time , A= amount of substance at time t , Ao= amount of substance at time 0
therefore at t=8 hours , A=16.5 gr
Ao = A*2^(t/T) = 16.5 g * 2^(8 hours/3.20 hours) = 93.338 g
Ao = 93.338 g
