The formula for determining the area of a rectangle is expressed as
Area = length * width
From the diagram,
Length = 3x + 6
Width = 4x - 1
The expression for the area of the room would be
![\begin{gathered} (3x\text{ + 6)(4x - 1) = (3x }*\text{ 4x) + (3x }*-\text{ 1) + (6 }*4x)\text{ + (6}*-1) \\ \text{Area = 12x}^2\text{ - 3x + 24x - 6} \\ \text{Area = 12x}^2\text{ + 21x - 6} \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/high-school/ucrgeimwkh92zebhin2m5os1v5t39k5z1l.png)
In standard polynomial form, the terms are arranged in decreasing order of exponents. Therefore, the expression in standard form is
![12x^2\text{ + 21x - 6}](https://img.qammunity.org/2023/formulas/mathematics/high-school/n64wtz34lhgx5szdb47vnh9aw4xoqc11pr.png)