triangle

1/2*4*13=26

area of shaded region is called x.

Total area minus blank region= x

lets call area of blank region y

lets call total area z

$z-y=x$

$z = (12\times9)/2$

$z=54$

$y=\frac{12\times5}{2}$

$y=30$

Plug them in to get

$54-30=x$

$x=24$

Here's another way: 

The area of the 2 triangles is $12 \times (5 + 4) \div 2 = 54$

The area of the white triangle is $12 \times 5 \div 2 = 30$

This means that the area of the shaded region is $54 - 30 = \color{brown}\boxed{24}$