Area of a rectangle is equal to length times width so the equation:
\(A = lw\)
To find w, you would solve for it in this equation by dividing by l on both sides like so:
\(\frac{A}{l}= \frac{lw}{l}\)
Which leaves you with:
\(w = \frac{A}{l}\)
So to find width you divide the Area by the length:
\(w = \frac{A}{l}\)
