documentclass[12pt]{article}
usepackage{amsmath}
usepackage{cleveref}
usepackage[letterpaper]{geometry}
begin{document}

begin{flalign}
&f(x) geq g(x)& label{i:positivity}
end{flalign}

Admitting that cref{i:positivity} has a solution, ...

end{document}