with me, but I had to improve it as it was in accordance with the
previous settings and improper use of LaTeX. I had used  too many
dollar(\$) sign, which is not good to use as it tells LaTeX to do the
things forcibly. So, I had to clean-up the code for that. Also I had
lot of equations, so I just made some packages as the primary one.
Like:

1) flushleft
2) eqnarray
3) align
4) alignat

Flushleft will apply left aligning setting in all equations, and to
ident some of the lines I used \hspace.
We have monoeuations(single equal to(=)), bi-equations. For
monoequations align is used.
Coming to eqnarray and alignat, they are almost the same but with some
notable differences:

• eqnarray has two alignment points (it’s basically just array with a
default preamble) whereas align has one. x + y &=& z versus x + y &= z
• eqnarray changes the spacing at the alignment points depending on
different factors whereas align keeps it fixed (which is generally
what you want)
• eqnarray allows page breaks between lines and align doesn’t

Using them I fulfilling the needs of the book.