Answer:
18 square feet.
Explanation:
To find the area of the grassy region we have to find the difference between the whole area and the doghouse area, where whole area refers to grassy area plus doghouse area.
Doghouse area:
Due to its rectangular form, its area would be:

Whole area:

Observe that the whole are includes 1 feet on each side.
Grassy area:
Now, the difference between the whole area and the doghouse area would give us the grassy region:

Therefore, the grassy region is 18 square feet.