Answer
The solution set is empty.
Work Step by Step
$4x^2+9<6x$, I subtract $6x$ from both sides, hence $4x^2-6x+9<0$, its determinant ($b^2-4ac=(-6)^2-4\cdot4\cdot9=-108$) is less than $0$, hence it cannot be less than $0$ (also because its leading coefficient, $4$ is bigger than $0$), hence the solution set is empty. (also see the graph of $4x^2-6x+9$)
