66810*(1-0.5)^x=3.4 . . . 66810*(0.5)^x=3.4 . . . 0.5^x=3.4 / 66810=0.00005089058524 . . . log(0.5^x)=log(5.08905*10-5) . . . x*log(0.5)=log(.............) . . . x=log(.........) / log(0.5) . . . x= -4.293362555 / -0.301029995 . . . x=14.262241724450083