Answer:
The approximate difference in the half-lives of the isotopes is 66 days.
Step-by-step explanation:
The decay of an isotope is represented by the following differential equation:

Where:
- Current mass of the isotope, measured in kilograms.
- Time, measured in days.
- Time constant, measured in days.
The solution of the differential equation is:

Where
is the initial mass of the isotope, measure in kilograms.
Now, the time constant is cleared:


The half-life of a isotope (
) as a function of time constant is:


The half-life difference between isotope B and isotope A is:

If
,
and
, the difference in the half-lives of the isotopes is:


The approximate difference in the half-lives of the isotopes is 66 days.