Answer
$x=\frac{21}{4}$
Work Step by Step
We are given the equation $\frac{x}{3}+7=\frac{5x}{3}$.
Then equation is then incorrectly simplified to $x+7=5x$.
In order to eliminate the fractions, we must multiply all terms by 3, not just the terms with fractions.
$x+21=5x$
In order to simplify the equation from here, we can subtract x from both sides.
$21=4x$
Divide both sides by 4.
$x=\frac{21}{4}$
Note: The equation is also incorrectly simplified after $7=4x$. Dividing both sides of this equation would result in $x=\frac{7}{4}$.