Let be N =8,000., an No =<span>15,500, we have N = No e^ -k.T k= </span><span>3% =3/100 T= periode of time when T=t, N=No=8,000 so 8000=15,500 </span>e^ -(3/100).t 8000 / 15,500 =e^ -(3/100).t, 0.51 = e^ -(3/100).t, and Ln(0.51) = -3/100.t implies t= [100x Ln(0.51)] /3= 22, 04 years