#### Answer

$8x^2-12x+4$

#### Work Step by Step

Step 1. Let the length be $y$ units; we have the area as $(x+\frac{3}{4})y=8x^3-6x^2-5x+3$, which gives $y=\frac{8x^3-6x^2-5x+3}{x+\frac{3}{4}}$
Step 2. Using synthetic division as shown in the figure, we have $y=8x^2-12x+4$$