Iam very confused what is the area of this composite figure. sorry for bad photo. .

Divide the figure using vertical lines into 3 sub-areas.  You have already done this on the left side of the figure.  The base of this trapezoid is (30-10 -12) ft, or 8 ft.  The trapezoid has 2 heights shown:  one is 11 ft and the other is 15 ft.
The area of this trap. is  [ (11 ft + 15 ft)/2 ] * [8 ft]  ], or 13*8 ft^2, or 104 ft^2.

Next is the rectangle in the middle.  Its height is 15 ft and its width is 12 ft.  Its area is (15 ft)(12 ft) = 180 ft^2.

Last is the trapezoid on the right.  Its base is 10 ft and the average of its heights is [(15+7.5) ft] / 2, or  11.25 ft.  Thus, the area of this trap. is
(11.25 ft)(10 ft) = 112.5 ft^2.  

Add these 3 sub-areas together to get the total area.

Good luck!!

The slope of the function is 0.5.