\documentclass[12pt,leqno]{article}
\usepackage{mathtools}
\makeatletter %%
\renewcommand\tagform@[1]{\maketag@@@{\ignorespaces#1\unskip\@@italiccorr}} %% Удаляем () вокруг формулы
\makeatother %%
\renewcommand{\theequation}{\textbf{\arabic{equation}.}} %% делаем номер жирным и ставим точку
\begin{document}
\begingroup
\allowdisplaybreaks % разрешаем разбиение многолинейной формулы на страницы
\begin{align}
&\iint_D (x^3+y^3)\,dxdy &&D: ....\\
&\iint_D (x^3+y^3)\,dxdy &&D: ....\\
&\iint_D (x^3+y^3)\,dxdy &&D: ....\\
&\iint_D (x^3+y^3)\,dxdy &&D: ....\\
&\iint_D (x^3+y^3)\,dxdy &&D: ....\\
&\iint_D (x^3+y^3)\,dxdy &&D: ....\\
&\iint_D (x^3+y^3)\,dxdy &&D: ....\\
&\iint_D (x^3+y^3)\,dxdy &&D: ....\\
&\iint_D (x^3+y^3)\,dxdy &&D: ....\\
&\iint_D (x^3+y^3)\,dxdy &&D: ....\\
&\iint_D (x^3+y^3)\,dxdy &&D: ....\\
&\iint_D (x^3+y^3)\,dxdy &&D: ....\\
&\iint_D (x^3+y^3)\,dxdy &&D: ....\\
&\iint_D (x^3+y^3)\,dxdy &&D: ....\\
&\iint_D (x^3+y^3)\,dxdy &&D: ....\\
&\iint_D (x^3+y^3)\,dxdy &&D: ....\\
&\iint_D (x^3+y^3)\,dxdy &&D: ....\\
&\iint_D (x^3+y^3)\,dxdy &&D: ....\\
&\iint_D (x^3+y^3)\,dxdy &&D: ....\\
&\iint_D (x^3+y^3)\,dxdy &&D: ....\\
&\iint_D (x^3+y^3)\,dxdy &&D: ....\\
&\iint_D (x^3+y^3)\,dxdy &&D: ....\\
&\iint_D (x^3+y^3)\,dxdy &&D: ....\\
&\iint_D (x^3+y^3)\,dxdy &&D: ....\\
&\iint_D (x^3+y^3)\,dxdy &&D: ....\\
&\iint_D (x^3+y^3)\,dxdy &&D: ....\\
&\iint_D (x^3+y^3)\,dxdy &&D: ....\\
&\iint_D (x^3+y^3)\,dxdy &&D: ....\\
&\iint_D (x^3+y^3)\,dxdy &&D: ....\\
&\iint_D (x^3+y^3)\,dxdy &&D: ....\\
&\iint_D (x^3+y^3)\,dxdy &&D: ....\\
&\iint_D (x^3+y^3)\,dxdy &&D: ....\\
&\iint_D (x^3+y^3)\,dxdy &&D: ....\\
&\iint_D (x^3+y^3)\,dxdy &&D: ....\\
&\iint_D (x^3+y^3)\,dxdy &&D: ....\\
&\iint_D (x^3+y^3)\,dxdy &&D: ....\\
&\iint_D (x^3+y^3)\,dxdy &&D: ....\\
&\iint_D (x^3+y^3)\,dxdy &&D: ....\\
&\iint_D (x^3+y^3)\,dxdy &&D: ....\\
&\iint_D (x^3+y^3)\,dxdy &&D: ....\\
&\iint_D (x^3+y^3)\,dxdy &&D: ....\\
&\iint_D (x^3+y^3)\,dxdy &&D: ....\\
&\iint_D (x^3+y^3)\,dxdy &&D: ....\\
&\iint_D (x^3+y^3)\,dxdy &&D: ....\\
&\iint_D (x^3+y^3)\,dxdy &&D: ....\\
&\iint_D (x^3+y^3)\,dxdy &&D: ....\\
&\iint_D (x^3+y^3)\,dxdy &&D: ....\\
&\iint_D (x^3+y^3)\,dxdy &&D: ....\\
&\iint_D (x^3+y^3)\,dxdy &&D: ....\\
&\iint_D (x^3+y^3)\,dxdy &&D: ....\\
\end{align}
\endgroup
\end{document}