The radioactive decay follows first order kinetics
For first order reaction the relation between rate constant half life is
K = 0.693 / t1/2
K = 0.693 / 14 = 0.0495 day^-1
The first order rate equation is
ln (A / At) = Kt
Where
A = initial amount
At = amount left at time t
t = time
K = rate constant
Putting values
ln (6 / At) = 0.0495 X 112
ln (6 /At) = 5.544
taking antilog
6 / At = 255.7
At = 0.0235 g
