Q:

Aligning equations while using cases in align environment

I have the following code:
\begin{align}
& a+b+c+d+e+f = 15000 & \text{for } a = 1 ... 15  \\
& D_t= 
\begin{cases}
   \text{equation} , & \text{for } t = 1 ... 10 \\
   \text{another equation} , & \text{for } t = 1 ... 10 \\
\end{cases} 
\end{align}

This produces the following:

However, I would like the "for" arguments in cases to be aligned to those in the align environment, which would look something like:

I was wondering if there is a way of doing this automatically, rather than using manual spacing.  I have tried using arrays, however it didn't seem to solve the issue. 
Thank you. 

A:

The \Centerstack retains a settable but fixed baselineskip.   Thus, using \Centerstacks to set both the equations of the case, as well as (separately) the conditions of the case, will insure that their baselineskips are compatible. 
\documentclass{report}
\usepackage{amsmath}
\usepackage[usestackEOL]{stackengine}
\stackMath
\setstackgap{L}{1.2\normalbaselineskip}
\begin{document}
\begin{align}
& a+b+c+d+e+f = 15000 && \text{for } a = 1 ... 15  \\
& D_t= \left\{\Centerstack[l]{\text{equation} ,\\ \text{another equation}}\right.&& 
   \Centerstack{ \text{for } t = 1 ... 10 \\ \text{for } t = 1 ... 10}
\end{align}
\end{document}

A:

Here are two ways to obtain it:
\documentclass{article}
\usepackage{mathtools}

\begin{document}

\begin{alignat}{2}
& a+b+c+d+e+f = 15000 &\quad & \text{for } a = 1 ... 15 \\
& D_t=
\begin{cases}
   \text{equation} , \\
   \text{another equation} ,
\end{cases} & & \begin{aligned}
   \text{for } t = 1 ... 10 \\\text{for } t = 1 ... 10
\end{aligned}
\end{alignat}

\begin{alignat}{2}
& a+b+c+d+e+f = 15000 &\quad & \text{for } a = 1 ... 15 \\
& D_t=
\mathrlap{\begin{cases}
   \text{equation} , & \text{for } t = 1 ... 10 \\
   \text{another equation} ,\hspace{1.9em}& \text{for }t = 1 ... 10
\end{cases}}
\end{alignat}

\end{document} 

