The area of a square is it's length times it's width. Since in a square the length and the width are the same, the area is just the size of it's sides squared:
[tex]A=\text{side}^{2}[/tex]This square have sides of 6/7 yd, so the area is:
[tex]A=(\frac{6}{7}yd)^{2}=\frac{6^2}{7^{2}}yd^{2}[/tex][tex]A=\frac{36}{49}yd^{2}[/tex]