LaTeX: Alligning long equation and manually input equation number

If your equation is too long, you can insert the following comment in the equation environment, with the \\ to break line.

\begin{equation}
\begin{aligned}
 ..... \\
........
 \end{aligned}
\end{equation}

for example:

\begin{equation}\label{e10}
 \begin{aligned}
  \text{ln VA} = lnQ_3 + 1/ \sigma_y lnMP + lnA + \alpha lnK + (1-\alpha + \varepsilon)\\
   \times ln (N-a_0 N^{3/2}) + (1-\rho)/\rho((1+MS)^{-1} ln(N-a_0N^{3/2})).
 \end{aligned}  
\end{equation}


If you want to manually set equation number just put \tag{equation number} in the end of the equation:

\begin{equation}\label{e10a}
\begin{aligned}
 \text{ln VA} = lnQ_3 + 1/ \sigma_y lnMP + lnA + \alpha lnK + (1-\alpha + \varepsilon)\\
   \times ln (N-a_0 N^{3/2}) + (1-\rho)/\rho((1+MS)^{-1} ln(N-a_0N^{3/2})).
   \end{aligned}   \tag{10a}
\end{equation}