Let A be the area of the wall.
Given that the amount of paint needed to cover a wall paint is proportinal to ts area, and the wall is rectangular with area
[tex]A=6z^2+6z\text{ ---- equation 1}[/tex]Since the wall has a rectangular shape, the area of the wall is evaluated as
[tex]\text{Area of rectangular wall = length}\times width[/tex]From equation 1,
[tex]A=6z^2\text{ + 6z}[/tex]simplify by factorization,
[tex]A\text{ = 6z(z+1)}[/tex]Since the length has a longer dimension than the width, we have
[tex]\begin{gathered} \text{length = 6z} \\ \text{breadth = z+1} \end{gathered}[/tex]Hence, the possible expressions for the length and width of the wall are
[tex]\begin{gathered} \text{length = 6z} \\ \text{width = z+1} \end{gathered}[/tex]