Solve the equation
x+5+x+x+
x+x+x+5=
xx6xx( this is only addition not multiplication)
use 0-9 only once figure out the x

Note:
3x means 3 times x or x+x+x
xx means x times x or x(x)

so
x+5+x+x+x+x+x+5=x+x+6+x+x
add like terms
6(x)+10=4(x)+6
 not sure about the 0-9 part so I will disreagrd for now, please ask for correction later

6x+10=4x+6
subtract 4x from both sides
2x+10=6
subtract 10 from both sides
2x=-4
divide both sides by 2
x=-4/2=-2 (divide or multiply by different signs and get negative)
x=-2

side,s = 9cm

surface area of cube, a = 6s^2

a = 6 × 9^2 = 486 square centimetres