\documentclass[tikz, border=1mm]{standalone}
\usetikzlibrary{matrix,calc}

\colorlet{mongris}{gray!15}

\begin{document}
	\begin{tikzpicture}
		\matrix (M) [
		matrix of nodes,
		row sep =-\pgflinewidth,
		column sep = -\pgflinewidth,
		execute at begin cell=\strut,
		execute at empty cell={\node{\strut};},
		nodes={rectangle, draw, anchor=center, minimum width=5em,
			minimum height=6.3ex},
		column 1/.style={nodes={text width=2cm, align=center, fill=mongris}},
		]
		{
			Masse de chocolat & $100$ & $250$ & $350$ \\
			Masse de cacao    & $54$  & ?     & ?      \\
		};
		\begin{scope}
			\node[draw,circle,inner sep=1pt] (PLUS) at ([yshift=5mm]$(M-1-2.north)!0.5!(M-1-3.north)$) {$+$} ;
			\draw (M-1-2.north) to[out=90,in=180] (PLUS.west) ;
			\draw (M-1-3.north) to[out=90,in=0] (PLUS.east) ;
			\draw[->,>=latex] (PLUS.north) to[out=60,in=90] (M-1-4.north) ;
		\end{scope}
%		\begin{scope}[->, red!80!black, myshift/.initial=0.8ex]
%			\draw ([yshift=\pgfkeysvalueof{/tikz/myshift}]M-1-2.north) to[bend left]
%			node[above] {$\mskip-\medmuskip {} \times 2{,}5$}
%			([yshift=\pgfkeysvalueof{/tikz/myshift}]M-1-3.north);
%			\draw ([xshift=\pgfkeysvalueof{/tikz/myshift}]M-1-3.east) to[bend left]
%			node[ right] {$\! {} \times 0{,}54$}
%			([xshift=\pgfkeysvalueof{/tikz/myshift}]M-2-3.east);
%		\end{scope}
	\end{tikzpicture}
\end{document}