The applicable decay formula is:
N = No*e^(-kt)
Where
N = Mass left after time t
No = Original mass
k = constant
t = half life
Using the values given,
N/No = e^(-0.1446t) = 1/2
ln (1/2) = -0.1446 t *ln e^1
-0.6931 = -0.1446 t
t = 0.6331/0.1446 = 4.79 days
Therefore, half-life is 4.8 days.
