\documentclass[a4paper,10pt]{article}
\usepackage[utf8]{inputenc}
\newcommand{\theme}{Macdondalds}
\newcommand{\ttt}{D}
\newcommand{\topname}{Drink}
\newcommand{\mmm}{M}
\newcommand{\midname}{Burger}
\newcommand{\bbb}{F}
\newcommand{\botname}{fries}

%opening
\title{}
\author{}

\begin{document}

\maketitle

\begin{abstract}
This small document un~picks the common
facebook maths picture puzzle. % solution
\end{abstract}

\section{Various themes but always the same hidden multiply: this one is the {\theme} maths puzzle etc.}

Where $\ttt$ is a {\topname}, $\mmm$ is a {\midname} and $\bbb$ is {\botname}:

$$ \ttt + \ttt + \ttt = 30 $$
so $\ttt$ == 10
$$ \ttt + \mmm + \mmm = 20 $$
so $\mmm$ == 5
$$ \mmm + \bbb \bbb + \bbb \bbb = 9 $$
so $\bbb \bbb + \bbb \bbb = 4$ therefore $\bbb \bbb=2$ so $\bbb=\pm \sqrt{2}$

Onto the final equation
$$\mmm + \bbb \times \ttt = \; ? $$

As $\bbb$ is  $\pm \sqrt{2}$  there are actually two valid answers:
$ 5 + \sqrt{2} \times 10 $ and $ 5 - \sqrt{2} \times 10 $
So the answer is either 19.142 or -9.142.

\vspace{0.5cm}
typeset in {\LaTeX} on {\today}.
\end{document}

