Answer:
The area of the trapezium is 18 ft²
Explanation:
Given;
Two parallel sides of the polygon as follows;
The first parallel side = 1 ft + 4 ft = 5 ft
The second parallel side = 4 ft
If this polygon is rotated 90 degrees, it forms a trapezium with a height of 4 ft.
The area of a trapezium is calculated as;

Therefore, the area of the trapezium is 18 ft²