begin{center} text end{center}qquadhspace*{fill} number

documentclass{report}
usepackage{lipsum}

begin{document}
lipsum[1]
begin{center}
text here\
hfill{}text herehfillllap{(1)}\
text here
end{center}
lipsum[2]
end{document}

documentclass{article}
usepackage{amsmath}
usepackage{lipsum} % for context

newenvironment{numberedtext}[1]
 {begin{equation}tag{#1}begin{minipage}{0.9textwidth}centering}
 {end{minipage}end{equation}}

begin{document}

lipsum*[3]
begin{numberedtext}{1}
some text to be centered
end{numberedtext}
lipsum*[4]
begin{numberedtext}{42}
some other text
end{numberedtext}
lipsum[5]

end{document}