You need to remember what is the formula of the volume of the cube:
V = Area of the square base*height
You should remember that all the edges of a cube have equal lengths.
Let the lenght of the edge of the cube be x.
`V = x*x*x = x^3`
125 = `x^3 ` => `x = root(3) 125 ` => x = 5cm
The length of the side of the cube is x = 5cm.