# Latex, left margin align equation in a longtable [duplicate]

I've created a longtable in latex, and I've centred it, because it is quite wide, and I don't want my text running off the side. However I have one particularly long equation, which I put in the align block, so it goes down into a new line. However unlike the rest of the equations in column 1, it doesn't start at the same place as the others (which is the left of the margin).

I have tried using the same method as shown here, but that doesn't work. Latex longtable, start equation on new line

I'm wondering how I can make it start on at the margin, and also how to remove the [t]

My code and a print screen of my pdf is below:

As you can see from the picture above, column 1, row 5 (with the red text), the equation doesn't start at the same point as the others. And also the [t] is there. Any way to remove it would also be helpful.

\documentclass[10pt,a4paper]{article}
\usepackage{array,longtable}
\newcolumntype{L}{>{\centering}m{5cm}}
\setlength{\extrarowheight}{2.5mm}
\usepackage{graphicx}
\usepackage{fixltx2e}
\usepackage[margin=25mm]{geometry}
\usepackage[fleqn]{amsmath}
\usepackage{multicol}
\usepackage{multirow}
\usepackage{float}
\usepackage{xcolor}

% all relevant preamble above %

\begin{document}
...
...
\begingroup
\setlength{\LTleft}{-20cm plus -1fill}
\setlength{\LTright}{\LTleft}
\renewcommand{\arraystretch}{1.7}
\begin{longtable}{ >{$}l<{$} L >{$}l<{$} }
\centering
....
more similar
....

\overline{X} \cdotp Y \cdotp Z + [(\overline{X} + Y + Z) \cdotp (\overline{X} + \overline{Y} + \overline{Z})]  &
Multiply everything out} &
\begin{aligned}[t]
A \cdotp B = \overline{A} + \overline{B},
& \quad A = \overline{X} + Y + Z \\
& \quad B = \overline{X} + \overline{Y} + \overline{Z}
\end{aligned} \\

\begin{aligned}[l]
\overline{X} \cdotp Y \cdotp Z + [\textcolor{red}{\overline{X} \cdotp    \overline{X}} + \overline{X} \cdot \overline{Y} + \overline{X} \cdot \overline{Z} + \\
Y \cdotp \overline{X} + \textcolor{red}{Y  \cdot \overline{Y}} + Y \cdot \overline{Z} +
Z \cdotp \overline{X} + Z \cdot  \overline{Y} + \textcolor{red}{Z \cdot \overline{Z}}]
\end{aligned}[t] &
Use De Morgans's law [OR to AND] across 3 variables, twice. &
\overline{A+B+C} = \overline{A} \cdotp \overline{B} \cdotp \overline{C} \\
....
more similar rows
....
\end{longtable}
\endgroup
...
...
\end{document}