What's the relationship between the volume of the pyramid inscribed in a cube and the volume of the cube?

Let
x> the side length of the cube

we know that
[volume of a cube]=x³

[volume of a pyramid]=[area of the base]*h/3
area of the base=x²
h=x
[volume of a pyramid]=[x²]*x/3> x³/3
so

[volume of a pyramid]=[volume of a cube]/3

the answer is
[volume of a pyramid]=[volume of a cube]/3

First subtract 10 from both side
y^2+6y-16=0
(y+8)(y-2)=0
-8 and 2