Question 1150245
A=Aoe^(kt)
find k with half-life of 8 days, so A=0.5 Ao
0.5Ao=Aoe^8k
0.5=e^8k
ln both sides
-0.693=8k
k=-0.0866

Ao=6*A
so this becomes
ln(1/6)=e^(-0.0866t)
-1.7918=-0.0866t
t=-20.68 days if I round at the very end

This is about 2.5 half-lives, and 1/2.5^2 is 1/6.25 or about 1/6 as a rough check.