Answer
$ 10$ meters
Work Step by Step
The perimeter is the sum of the sides' lengths
$P=\displaystyle \frac{5x+10}{x+3}+\frac{5}{x+3}+\frac{5x+10}{x+3}+\frac{5}{x+3}$
To add/subtract rational expressions with the same denominator,
add/subtract numerators and place the sum/difference over the common denominator.
$P=\displaystyle \frac{5x+10+5+5x+10+5}{x+3}$
$=\displaystyle \frac{10x+30}{x+3}$
$=\displaystyle \frac{10(x+3)}{(x+3)}$
... common factors cancel,
=$ 10$ meters