Answer
$\displaystyle \frac{x^{2}-x+4}{3}$
Work Step by Step
When two rational expressions have the same denominator, we subtract like so:
$$ \frac{A}{C}-\frac{B}{C}=\frac{A-B}{C} $$
$\displaystyle \frac{x^{2}}{3}-\frac{x-4}{3}=\frac{x^{2}-(x-4)}{3}$= $\displaystyle \frac{x^{2}-x+4}{3}$
