Explanation:
hello,
you can find the area of the polygon by first dividing the diagram into smaller shapes.
in this case, you can divide the polygon into 2 rectangles - see attached.
thus,
a of polygon = a of rectangle A + a of rectangle B
a of polygon = ( l × w of A ) + ( l × w of B)
a of polygon = ( 18 ft × 9 ft ) + ( 8 ft × 12 ft )
a of polygon = 162 ft² + 96 ft²
= 258 ft²
please note that the width of rectangle A is 9 and not 21. it is so as:
width of A = 21 - 12
= 9 ft.
and width of B = 12 ft.
hope this helps you, au revoir!