The answer is

.
There is very similar question on Brainly, in which dimensions of the living room are given (20 feet, 30 feet).
So, knowing this, we first need to calculate how much 6% of the living room is.
The area of the living room is 600 square feet, since it is rectangle-shaped:
P = a * b = 200 feet * 30 feet = 600 square feet.
6% of 600 square feet is 36 square feet:
600 square feet : 100% = A : 6%
A = 600 * 6 / 100 = 36 square feet
The area of the triangular-based cabinet (A) is

, where a is the base, and h is the height of the triangle.
It is given:
A = 36
a = 2x + 3
h = 3x + 6
Now, let's implement this to the formula

:

⇒


Let's both sides divide by 3:

⇒

This is the quadratic formula (

) for which

or
<span>

.
</span>We will use only <span>

, because the length cannot have negative value.</span>
<span>From the equation

, we know that
</span>a = 2
b = 7
c = -18
Thus, <span>

:
</span>