Area of the shaded region = the area of the trapeze - the area of the triangle.
.
[tex]\displaystyle\\A=\frac{(32+17)\times21}{2}-\frac{11\times9}{2}\\\\A=\frac{49\times21}{2}-\frac{99}{2}\\\\A=\frac{1029}{2}-\frac{99}{2}\\\\A=\frac{1029-99}{2}\\\\A=\frac{930}{2}\\\\\boxed{\bf~A=465~mm^2}[/tex]
