Peter has 12 marbles, he gives 3 to Tom and 5 to Lily. How many does marbled does he have left??

4 marbles left.

$$\mbox{You\;are\;going\;finding\;how\;much\;marbles\;he\;gave\;to\;Tom\;and\;Lily.}\\\\5+3=8\\\\\mbox{Now,\;subtract\;the\;8\;marbles\;that\;he\;gave\;to\;Tom\;and\;Lily\;from\;the\;marbles\;that\;Peter\;had.}\\\\12-8=4$$

$$4\mbox{\;So,\;4\;is\;the\;answer.}$$

$$\mbox{Hope\;it\;helps!}$$

Hey, Dragon, I continue to be very impressed with your LaTex  ,  I think that I will give you thumbs up but it is for your LaTex not for your answer to the troll question.

EDIT: I just realised that you did use the \mbox function.  mbox stands for message box.  If you are in a mbox then you do not need to use \; to separate your words!  Just leave them out.  You only need to use \; to separate words is you are in math mode and you are not in math mode if you are in a mbox!

I also want to show you some other ways that you could have written this:

The first one I learned recently off Alan.  LaTex has 2 main modes. Normal and Math modes.  The forum is automatically set to math mode. This means that when we write a word the program thinks that you are just entering a string of pronumerals (letters) and it thinks the gaps mean nothing so it ignores them.  If you want the LaTex to recognise that you are NOT entering math then you can turn math mode off by entering $$ then it 'understands' that gaps etc mean something.  

When you want to enter a math thing you have to tell the program to turn the math mode back on again.  You do this by putting a $ one either side of it like $5+3=8$

If you have a lot of writing and a little bit of maths then this is a really nice way of doing it in LaTex 

$$ You are finding how much marbles he gave to Tom and Lily\\

$5+3=8$\\ Now subtract etc etc\\ $12-8=4$\\ etc

$$You are finding how much marbles he gave to Tom and Lily\\
$5+3=8$\\
Now subtract etc etc\\
$12-8=4$\\
etc$$

Do you understand all that Dragon?