Uprisings or move to another place with fertile soil
Union victory at Antietam, provided president Abraham Lincoln the opportunity he had wanted to announce the Emmancipation Proclamation.
The decay equation is of the form

where
m(t) = the mass remaining after t minutes
m₀ = the initial mass
k = constant
Because the half-life is 3 minutes, therefore

Therefore
-3k = ln(0.5)
k = ln(0.5)/(-3) = 0.231
Because m₀ = 16 mg, the time, t, for the mass to decay to 1.0 mg is given by

Answer: 22 min (nearest integer)