The shaded region is a parallelogram.
The formula for the area of any parallelogram is

.
The base of the parallelogram is 2 meters long (given).
The height of the parallelogram is 9 meters (do not be fooled by the unnecessary information of 14 meters)
The height is 9 meters because the height has to be perpendicular to the base. Thus, the side length must be 9 meters.
Multiply them together.

The area of the parallelogram is 18 square meters.
Hi there!
So, our two equations are:
2x + 3y = 20 and
-2x + y = 4
We can see that the x's will cancel out because they're the same number, opposite signs. Then we're left with 4y = 24.
Divide 24 by 4, which is 6.
y = 6, then we plug that in to the first equation for y:
2x + 3(6) = 20
2x + 18 = 20
2x = 2
x = 1
So, she made her first mistake when adding the equations, adding 20 and 4, she somehow got 16.
The solution to the system is (1,6).
I hope I helped!