Here we have to use the given formula of the half life which is
[tex] A(t) =A_{0} (0.5)^{t/h} [/tex]
A(t) is the amount remains after time,t, A0 is the initial amount and h represents the half life.
In the given question , initial amount is 150 grams, and half life is 123 days .
So the required expression is
[tex] A(t) = 150(0.5)^{t/123} [/tex]
In the second part, we have to find the amount remaining after 365 days.
So we put t=365 .
[tex] A(t) =150(0.5)^{365/123} = 19.18 grams . [/tex]