#### Answer

$30x^2$

#### Work Step by Step

Let A be the area of the bigger triangle. Hence, A = $\frac{1}{2}(9x)(12x)=54x^2$
Let B be the area of the smaller triangle. Hence, B = $\frac{1}{2}(6x)(8x)=24x^2$
Subtract B from A.
Answer = A - B = $54x^2 - 24x^2 = 30x^2$