The formula represents the surface area s of a cube with side lengths x.
(choices in photo)

We have the following expression:
 S = 6x ^ 2
 We must clear x from the equation.
 For this, we follow the following steps:
 Step 1)
 Pass 6 to divide:
 S / 6 = x ^ 2
 Step 2)
 Square root on both sides:
 +/- root (S / 6) = x
 Step 3)
 Multiply numerator and denominator by 6:
 x = + / - root (6S / 6 * 6)
 Step 4)
 Rewrite expression:
 x = + / - root (6S / 36)
 Step 5)
 Take root to denominator:
 x = + / - (root (6S)) / 6
 
 x = + / - (root (6S)) / 6
 (option 2)

Dwould be the answer