a cube-shaped cat hideaway is 8ft cubed. On 3 sides there is a 1 ft opening. What is the area in fractions of the surface area that is not an opening?

You are given that the volume of the cube-shaped hideaway is 8 ft^{3}.The volume of a cube is $s^3$ where ss is the side length so ${\displaystyle s^3=8}$. Cube rooting both sides gives ${\displaystyle s=3\sqrt{8}=2}$ so the side lengths of the cube are s=2 ft.
The surface area of a cube is ${\displaystyle 6s^2}$ where ss is the side length. Since the side length is s=2 ft, then the total surface area of the cube including the openings is ${\displaystyle 6{\left(2\right)}^2=6\left(4\right)=24f{t}^2.}$
If each opening has a length and width of 1 ft, then each opening has an area of ${\displaystyle 1\times 1=1f{t}^2}$. Since there are 3 openings, then the total area of the openings is ${\displaystyle 3\times 1=33\times 1=3f{t}^2.}$
The surface area of the cube that is not openings is then ${\displaystyle 24f{t}^2-3f{t}^2=21.}$
The fraction of the surface area that is not an opening is then:
surface area that is not openings/total surface area${\displaystyle =\frac{21f{t}^2}{24f{t}^2}=\frac{7}{8}}$