Here the only limitation on the domain exists when the denominator is equal to zero, as division by zero has no meaning and is not "allowed" because of its meaninglessness. :)
Factor the denominator to find the excluded values of x...
3x^2+5x-12
3x^2+9x-4x-12
3x(x+3)-4(x+3)
(3x-4)(x+3)
So x CANNOT equal 4/3 or -3 (all other real values of x are part of the domain) so the domain is:
