alignment and numbering of math formulas

Question

I have 3 formulas which should be aligned at the = sign and numbered (1) to (3).

Seems a simple task but trying both \being{equation} with \begin{split} and \being{align} did not work out. I alwasy struggled with the numbering or wit the alignment. Never got it right.

For example my simple equations good look like:

a = x  + y     (1)

b = z - k      (2)

c = j x (z-k)  (3)
  = j x b

Answer 1

Here is specialised numbering and spacing as requested in the comments:

\documentclass{amsart}

\begin{document}
\begin{align}
  a &= x + y \tag{1}\\[2ex]
  b &= z - k \tag{2}\\[2ex]
  c &= j x (z-k) \tag{3}\\
    &= j x b \notag
\end{align}
\end{document}

You can change the value 2ex to increase or decrease the spacing.

To get equation numbers on the right instead of the left, use the reqno option to the documentclass amsart (or to the package amsmath if you are not using an ams class).

Answer 2

\begin{align}
 a &= x  + y \\
 b &= z - k \\
 c &= j x (z-k) \\
   &= j x b \notag
 \end{align}

That's how I've always done it and it works for me.