A good answer might be:

11 plus the number of pins in 10 rows.

Base Case

This keeps on going. Each round divides the problem into an integer and a problem that is smaller by one. Eventually you reach the end: 

number of pins in 12 rows = 12 + number of pins in 11 rows
number of pins in 11 rows = 11 + number of pins in 10 rows

                        . . .

number of pins in  3 rows =  3 + number of pins in 2 rows
number of pins in  2 rows =  2 + number of pins in 1 row
                          =  2 + 1

The number of pins in 1 row is called a base case. A base case is a problem that can solved immediately. In this example, the number of pins in 1 row is 1.

QUESTION 5:

In the "destroy a rock" problem of the previous chapter, what was the base case?