Count the number of small squares in each grid and write the total in the box next to 'A'.

The grid has 3 rows and 3 columns.
Number of squares = $3 \times 3 = 9$.
The box already contains 9.

The grid has 2 rows and 5 columns.
Number of squares = $2 \times 5 = 10$.
The box already contains 10.

The grid has 2 rows and 10 columns.
Number of squares = $2 \times 10 = 20$.
The first box is empty, and the second box already contains 20.
The answer for the first empty box is $\boxed{\text{20}}$.

The grid has 5 rows and 2 columns.
Number of squares = $5 \times 2 = 10$.
The box is empty.
The answer for the empty box is $\boxed{\text{10}}$.

The grid has 1 row and 10 columns.
Number of squares = $1 \times 10 = 10$.
Both boxes are empty.
The answers for the empty boxes are $\boxed{\text{10}}$ and $\boxed{\text{10}}$.

The grid has 2 rows and 4 columns.
Number of squares = $2 \times 4 = 8$.
The box already contains 8.

Here are the completed answers for the empty boxes:

• 3: A $\boxed{\text{20}}$
• 4: A $\boxed{\text{10}}$
• 5: A $\boxed{\text{10}}$ A $\boxed{\text{10}}$