Question

the length of a rectangle is 3 units shorter than one-third of the width, x. What is the expression.

Answer 1

One third of a certain quantity x means

$\dfrac{1}{3} x$

The length is 3 unit shorter than this, which means 3 less:

$\dfrac{1}{3} x - 3$

So these are the dimensions:

$\begin{cases} w = x\\l=\dfrac{1}{3} x - 3\end{cases}$