Area of the shaded region is 223.72 square units.
Explanation:
Area of the shaded region = Area of parallelogram - Area of triangle
Area of the parallelogram = base x height
 = 23.8 x 15
 = 357 square feet
Area of triangle = \frac{1}{2} 
2
1
 x base x height
Let the height of the triangle be represented by h, applying the Pythagoras theorem;
23.8^{2}23.8 
2
 = 21^{2}21 
2
 + h^{2}h 
2
 
566.44 = 441 + h^{2}h2
 h^{2}h 
2= 125.44
h = \sqrt{125.44} 
125.44
 = 11.2
h = 11.2
Area of the triangle = \frac{1}{2} 
21 x 23.8 x 11.2 = 133.28
Area of shaded region = 357 - 133.28
 = 223.72
Area of the shaded region is 223.72 square units.