The length of a rectangle is 4cm more than twice it's width .The perimeter of the is 40cm . Formulate an equation to determine the dimensions of the rectangle

Let $w$ be the width of the rectangle in cm.
Let $l$ be the length of the rectangle in cm.

"The length of a rectangle is 4cm more than twice its width."

The perimeter $P$ of a rectangle is given by $P = 2(l + w)$.
We are given that the perimeter is 40 cm.

This is the equation to determine the dimensions of the rectangle.