Isotope
is half life in year
.
Find the initial quantity :
\Half life to find
.
The general form of carbon isotope initial quantity is
, where,
is
and
is
.
.

Apply ln on both sides.
\
Substitute plug for
for
and
for
and
in the general form.

To find the Amount after
years:
General form is 
Substitute
and
in the 

Therefore, the amount after
years is
.
The initial quantity is
.
The amount after
years is
.