toxic radioactive substance

A. Between 2005 and 2008​, the average rate of inflation was about 3.6​% per year.

If a cart of groceries cost ​$110 in​ 2005, what did it cost in 2008​?

A cart of groceries cost approximately ​$____in 2008.

B.   A toxic radioactive substance with a density of 7
milligrams per square centimeter is detected in the ventilating ducts of a nuclear processing building that was used 55 years ago. If the​ half- life of the substance is 20 ​years, what was the density of the substance when it was deposited 55
years​ ago?

The density of the radioactive substance when it was deposited 55 years ago was approximately was approximately_____mg/ cm squared