How to use gather and aligned with multiple labels?

Question

1. The code below gives me ?? when referencing the equations. How do i fix it ?

2. How do I get (1a,1b) for the first equation if possible?

MWE

\documentclass{article}
\usepackage{amsmath}
\begin{document}

\begin{gather}
f: A \to B, g: B \to C \label{eq:1} \\
\begin{aligned}
f(a) &= \ldots \label{eq:2} \\
g(b) &= \ldots \label{eq:3}
\end{aligned}
\end{gather}

\ref{eq:1} \ref{eq:2} \ref{eq:3}

\end{document}

Answer 1

It is then better to use align. If you do not want the first equation to be aligned with the others, then it is possible to use \mathclap from mathtools package

Off-topic: cross referencing is better handled with cleveref package

\documentclass{article}

\usepackage{amsmath}
\usepackage{mathtools}
\usepackage{cleveref}

\begin{document}
    
    \begin{align}
        & \mathclap{f: A \to B, g: B \to C} \label{eq:1}
        \\
        f(a) &= \ldots \label{eq:2}
        \\
        g(b) &= \ldots \label{eq:3}
    \end{align}
    
    \cref{eq:1,eq:2,eq:3}
    
    \ref{eq:1} \ref{eq:2} \ref{eq:3}
    
\end{document}