I need help it’s hard personally

Half the length of the square is the radius of the circle as the length of the square is the diameter of the circle.
So, x/2 is the radius of the circle.

pi x r^2= Area of the circle
pi x (x/2)^2= 56 cm^2
(x/2)^2=56/pi
(x/2)^2=17.825
x/2 = root over 17.825
x/2 = 4.222
x=4.222 x 2
x= 8.444 = 8.44 cm (rounded to 3 significant figures).