We can calculate the area of the backyard as the sum of the area of the triangle and the rectangle.
The area of the rectangle is the product of its length and its width:
The area of the rectangle is 15 square feet.
Now, we can calculate the area of the triangle, which is half the product of its length and its height:
Then, the total area of the backyard is:
Answer: the area is 35 square feet.