\documentclass{article}
\usepackage{amsmath}
\usepackage{amssymb}
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\begin{document}
\[
h = \varphi \cdot 100 \sqrt{3} = \dfrac{28}{10 \sqrt{3}} \cdot 100 \sqrt{3} =
\dfrac{2800 \sqrt{3}}{10 \sqrt{3}} = 280\ cr
\]
\end{document}

