we know that
The perimeter of a square is equal to
[tex]P=4b[/tex]
where
b is the length side of a square
In this problem we have
[tex]b=(x+3)\ units\\P=48\ units[/tex]
substitute in the formula
[tex]48=4(x+3)[/tex]
Solve for x
[tex]12=(x+3)[/tex]
[tex]x=12-3=9\ units[/tex]
therefore
the answer is
The value of x is [tex]9\ units[/tex]
