Fred has a piggy bank. On his twelfth birthday, he started saving money. Every week, on the first day of the week, he puts half of his $ 40 allowance into the bank. Write a formula for , the amount of money in his piggy bank days after his twelfth birthday, on the domain . You may assume that Fred's first deposit was made on his birthday, i.e. on day , which is on the first day of the week.

a) Fill in the missing values in the table below.


b) Which of the following graphs is a graph of the function ?

A   B   C   D

(Click on a graph to enlarge it)