Are there any answers to choose from?
In a culture everyone need to think that there is a person spiritually bigger then them to help them with life. For example at funerals people pray to their god hoping the person makes it into the sanctuary, and because everyone wants to go to a sanctuary they follow as they believe there god will bring them to sanctuary if they comply to what their god says.
Set this up as
10 = 40 (1/2)t/28
and solve for t in years.
10/40 = (1/2)t/28
log(0.25) = (t/28) log(0.5)
t = 28 log(0.25) / log(0.5) years = 56 years
Test the answer:
56 years = 2(28 years) = 2 half-lives, so the remaining amount should be 1/2 of 1/2 of the initial amount, i.e. 1/4 of the initial amount, and 10 mg = 1/4 of 40 mg.
It depends on the mass of the ice,temperature around it and latent heat energy required to melt the ice.
However the furthest a ice berg can travel is estimately 32-40°n/s