I want to do something like this: 

![enter image description here](https://i.stack.imgur.com/qhYnY.png)

in a line with text, not center. Also I can control the left brace but it doesn't seems good. 

My MWE is:

```
\documentclass{article}
\usepackage{amsmath,cancel}
\newcommand\MyLBrace[2]{%
\left\{\rule{0pt}{#1}\right.\text{#2}}\newcommand\numberthis{\addtocounter{equation}{1}\tag{\theequation}}
\begin{document}
   Add m.t.m $\MyLBrace{5ex}{
   \begin{tabular}{r}
   21x\;-\;\cancel{6y}=24\\ 
   4x\;+\;\cancel{6y}=26 \\ \hline
   25x=50\\x=2\;\, 
  \end{tabular} }$
\end{document}

```

which result in this: 

![enter image description here](https://i.stack.imgur.com/SfvoP.png)

Any help, please?