is it
[tex] \frac{1}{3y} + \frac{1}{4} = 5[/tex]
or
[tex] \frac{1}{3} y + \frac{1}{4} = 5[/tex]
?
both start out the same, just remember what you do to one side you have to do to the other, so subtract both sides by 1/4, then you want to get y alone, so either divide or multiply the 3 on both sides! let me know which it is and I can help you out more
[edit] it's the second, and not going to use cross multiplication.
added a picture that walks you through it :)