Question

Wot it's the missing number x9=6x3

Answer 1

If i'm understanding this question correctly, i believe that it's 2. 
2*9=6*3

Answer 2

$x^9=6x^3 :|\text{Solve}$ 

$x^9-6x^3=0$ 

$x^3(x^6-6)=0$ 

$x=0,(+)(-) \sqrt[6]{6}$