#### Answer

perimeter = $14$ meters

#### Work Step by Step

RECALL:
(1) The perimeter of a polygon is equal to the sum of the lengths of all its sides.
(2) A square has four equal sides.
This means that the three unknown side lengths of the square are all $3.5$ meters.
Add the lengths of all the sides to find the perimeter:
perimeter = $3.5+3.5+3.5+3.5= 14$ meters.