Final answer = 558
Step-by-step explanation
Area of rectangle = L x B
Area of triangle = 1/2(b x h)
Area of rectangle = 28 x 21 =588
Area of triangle = 1/2(base x height)
base =(21-16) = 5
height =(28-16) = 12
Area of triangle = 1/2 x 5 x 12 = 30
Area of shaded portion = 588 - 30 =558
Hope it helps