Answer
The perimeter of the rectangle is $4x+400$.
Work Step by Step
We are given that the length of the rectangle is $x+200$ and the width is x.
And the formula for the perimeter of the rectangle is as follows:
$P=2\left( l+b \right)$.
Substituting the values of length and width of the given rectangle, we get:
$\begin{align}
& P=2\left( x+200+x \right) \\
& =2\left( 2x+200 \right) \\
& =4x+400
\end{align}$.
Thus, the algebraic expression to model the perimeter of the rectangle is $4x+400$.
