IF anyone can get x alone for the answer is god among men.
x/4 + 3/5 = 6
Please don't post so many responses yourself when you haven't given someone a chance to reply. Put everything you need in the FIRST post. And if you have added info, you can edit it. (Do not edit it if someone else has replied though.)
You do not need to find the lowest common denominator or anything like that.
(By the way, fractions are my best friend. They are the best way to express exact values.)