Question 1005174
N=Noexp(kt)
6.6=1.6exp(4k)
4.125=exp(4k)
ln of both sides
4k=1.4170.
without rounding k=0.3543 (now round)
1.6*e(9*.3543)=38.799 million
90/1.6=exp(0.3543t)
17.45=0.3543t,
ln of both sides
8.070 days.
The first thing you need to do is set up the exponential equation with some constant k of exponentiation.  Then solve for the constant using the data.  You have to take ln of both sides, because that removes the exp part.  You then look for the other variable, time, once you know what the constant is.