3. In a rectangle of size $7 \times 9$ cells, some cells contain one baby squirrel each, such that in every rectangle of size $2 \times 3$ (or $3 \times 2$) there are exactly 2 baby squirrels. Draw how they can be seated.
Answer. For example, like this (21 squirrels sit in the shaded cells).

![](https://cdn.mathpix.com/cropped/2024_05_06_7976d8a667797e2cc004g-3.jpg?height=469&width=580&top_left_y=2084&top_left_x=818)

Comment. A correct example - 20 points.