Ellie made a cube-shaped cardboard box with side-length s. the area of cardboard she used is given by the formula a = 6s2, where s represents the side length of the cube.

The correct question is 
Ellie made a cube-shaped cardboard box with side-length s. The area of cardboard she used is given by the formula A = 6s2, where s represents the side length of the cube.

Which equation correctly solves the formula for s?

we know that
A = 6s²> clear the variable s
s²=A/6> applying square root both members
s=√(A/6)> s=(1/6)*√(6*A)

the answer is
s=(1/6)*√(6*A)