We first have to find the perimeter of the triangle.
Since it's a equilateral triangle, which means all the sides of the triangle is the same length.
Perimeter of triangle = 7 x3
= 21
And there r 4 sides in a square,
So just divide 21 by 4
21 ÷ 4 = 5.25
So the answer is 5.25 cm