$\displaystyle \frac{3}{4}$
Oh I got it now, thx! I'll try to write the whole thing now
I forgot to wrap up with a ")", and the end was'nt right. But I'm improving, thx. My pc dies now, I have no charger, I hope to get more help from you later. Thank you so much for your patience!
First, you have to start and end with [ t e x ] and [ \ t e x ] tags- without the spaces, which I put on so it would not be interpreted as "Latex" tags and so you could see them. Also you need to put the numerator and denominator in "braces", { }. [ t e x ]\frac{3}{4}[/ t e x] without the spaces gives $\displaystyle \frac{3}{4}$.
There is a Latex tutorial at Physicsforums FAQ