Multiply both sides by 6x.
I'm guessing that what you intended to state is this:
If that be the case, what you call "cross multiply" would work just fine.
Remember to use parentheses to separate numerators and denominators. What you actually have written is:
in which case wonderboy1953's suggestion should be followed.
Please notice that it is not, and should not be, a matter of what you are "supposed" to do! You can, if you like, 'eliminate the denominators' just because fractions are difficult to work with! And a good way of doing that is to "cross multiply". You are still at the level of "following rules" rather than "thinking". Try to get to the level of thinking out a problem rather than just following rules- because there are always problems where the rules don't apply!