Answer:
The area that is left for development in the field outside the playground is 576 ft².
Explanation:
To calculate the area left for development in the field outside the playground, we need to subtract the area of the smaller rectangle from the area of the larger rectangle.
The area of a rectangle is the product of its width and length:

The dimensions of the larger rectangle are:
- width = 21 ft
- length = 36 ft
The dimensions of the smaller rectangle are:
- width = 15 ft
- length = 12 ft
Therefore, the development area can be calculated as follows:

Therefore, the area that is left for development in the field outside the playground is 576 ft².