Geometry help please

Given
A right angle triangle is removed from the rectangle to create the shaded region.
That is,
To find: The area of the shaded region.
Explanation:
It is given that,
That implies,
The area of the shaded region is,
[tex]\begin{gathered} Area\text{ }of\text{ }the\text{ }shaded\text{ }region=Area\text{ }of\text{ }the\text{ }rectangle-Area\text{ }of\text{ }the\text{ }triangle \\ =l\times b-\frac{1}{2}\times b\times h \\ =5\times9-\frac{1}{2}\times4\times3 \\ =45-6 \\ =39ft^2 \end{gathered}[/tex]Hence, the area of the shaded region is 39ft^2.