If you mean this:

then x = 0. The property in play here is the following: Any number raised to the "0" power is equal to "1". In this case, we would need to set the exponent of 3x = 0 and solve for x...
If you mean the equation:

then to solve for x(your blank), simply divide both sides of the equation by

:
You would have x =

this can also be written as
