check the picture below.
since we know the acute angle is 45°, that angle with the bottom base and the slanted line and the altitude make a 45-45-90 triangle, and thus we can get the value of that section at the bottom, as you see in the picture, thus the longer base is 9 + 18 + 9, or 36.
[tex]\bf \textit{area of a trapezoid}\\\\
A=\cfrac{h(a+b)}{2}~~
\begin{cases}
a,b=\stackrel{bases}{parallel~sides}\\
h=height\\
---------\\
a=18\\
b=36\\
h=9
\end{cases}\implies A=\cfrac{9(18+36)}{2}
\\\\\\
A=\cfrac{9(54)}{2}\implies A=243[/tex]
