First, we figure out the area of the wall, which is shaped like a trapezoid. The equation for the area of a trapezoid is

where a is the top base, b is the bottom base and h is the height.
Substitute your given values into the equation and solve:
A=1/2(12+15)9
A=4.5(27)
Area of the wall= 121.5ft²
Now we figure out the area of the of the circular window. The formula for the area of a circle is

where r is the radius
Substitute your given values into the equation and solve:
pi×3²

Now finally minus the area of the window from the area of the wall.
121.5-28.27433388=93.22566612
To 1 d.p., the area of the wall without the window is 93.2ft²