#### Answer

$L=W-\dfrac{NR-Nr}{400}$

#### Work Step by Step

$\bf{\text{Solution Outline:}}$
To solve the given equation, $
R=r+\dfrac{400(W-L)}{N}
$ for $
L
,$ use the properties of equality to isolate the variable.
$\bf{\text{Solution Details:}}$
Using the properties of equality to isolate the variable, the equation above is equivalent to
\begin{array}{l}\require{cancel}
R=r+\dfrac{400(W-L)}{N}
\\\\
N(R)=N\left( r+\dfrac{400(W-L)}{N} \right)
\\\\
NR=Nr+400(W-L)
\\\\
NR-Nr=400(W-L)
\\\\
\dfrac{NR-Nr}{400}=\dfrac{400(W-L)}{400}
\\\\
\dfrac{NR-Nr}{400}=W-L
\\\\
L=W-\dfrac{NR-Nr}{400}
.\end{array}