Answer
$4$
Work Step by Step
Divide both sides by $3$:
$\dfrac{3\sqrt{x}}{3}=\dfrac63$
$\sqrt{x}=2$
Square both sides:
$(\sqrt{x})^2=2^2$
$x=4$
Substitute into original problem to check for extraneous solutions:
$3\sqrt{4}=6$
$3\cdot2=6$
$6=6$
