begin{tikzpicture}
draw[gray!50, very thick,, fill = blue!30,rounded corners]
(0,0) rectangle (2.5,1.5)node[pos=.5]{$begin{array}{c}text{textcolor{blue!75}{textbf{Combinatorial}}} \ text{textcolor{blue!75}{textbf{Problem}}}end{array}$}
;
draw[->, thick, blue] (2.7,0.75) -- (3.8,0.75)
;
draw[gray!50, very thick, fill = blue!30,rounded corners]
(4,0) rectangle (6.5,1.5)node[pos=.5]{$begin{array}{c}text{textcolor{blue!75}{textbf{Boolean}}} \ text{textcolor{blue!75}{textbf{Expression(s)}}}end{array}$}
;
draw[->, thick, blue] (6.7,0.75) -- (7.8,0.75)
;
draw[gray!50, very thick, fill = blue!30,rounded corners]
(8,0) rectangle (10.5,1.5)node[pos=.5]{$begin{array}{c}text{textcolor{blue!75}{textbf{Conjuctive}}} \ text{textcolor{blue!75}{textbf{Normal Forms}}}end{array}$}
;
draw[->, thick, blue] (9.75,-0.2) -- (9.75,-0.-1.8)
;
draw[gray!50, very thick,, fill = blue!30,rounded corners]
(0,-3.5) rectangle (2.5,-2)node[pos=.5]{$begin{array}{c}text{textcolor{blue!75}{textbf{Problem}}} \ text{textcolor{blue!75}{textbf{Solution}}}end{array}$}
;
draw[<-, thick, blue] (2.7,-2.75) -- (3.8,-2.75)
;
draw[gray!50, very thick, fill = blue!30,rounded corners]
(4,-3.5) rectangle (6.5,-2)node[pos=.5]{$begin{array}{c}text{textcolor{blue!75}{textbf{Assignment of}}} \ text{textcolor{blue!75}{textbf{Variable(s)}}}end{array}$}
;
draw[<-, thick, blue] (6.7,-2.75) -- (7.8,-2.75)
;
draw[gray!50, very thick, fill = blue!30,rounded corners]
(8,-3.5) rectangle (10.5,-2)node[pos=.5]{$begin{array}{c}text{textcolor{blue!75}{textbf{SAT}}} \ text{textcolor{blue!75}{textbf{Solvers}}}end{array}$}
;
end{tikzpicture}

documentclass[tikz,border=3.14mm]{standalone}
usepackage{amsmath}
usetikzlibrary{matrix,shapes.arrows,shadows.blur}
begin{document}
begin{tikzpicture}[box/.style={align=center,text width=2.7cm,
text=blue!75,fill = blue!30,rounded corners,draw=gray!50,
very thick,font=bfseries,minimum height=1.5cm,minimum width=2.7cm,blur shadow},
arr/.style={single arrow,fill=blue!40,draw=blue,thick,blur shadow,minimum height=2em,
single arrow head extend=3pt}]
matrix[matrix of nodes,nodes={box,anchor=center},column sep=1.2cm,row sep=1.2cm] (mat) {
 {Combinatorial \
 Problem}
 &
 {Boolean \
 Expression(s)}
 &
 {Conjuctive \
 Normal Forms}
 \
 {Problem \
 Solution}
 &
 {Assignment of \
 Variable(s)}
 &
 {SAT \
 Solvers} \
};

path foreach X [count=Y] in {2,3}
 {(mat-1-Y) -- (mat-1-X) node [midway,sloped,arr] {}
  (mat-2-Y) -- (mat-2-X) node [midway,sloped,arr,shape border rotate=180] {}};
path (mat-1-3) -- (mat-2-3) node [midway,sloped,arr] {};
end{tikzpicture}
end{document}

documentclass[tikz,border=3.14mm]{standalone}
usetikzlibrary{matrix,shapes.arrows,shadows.blur}
definecolor{myblue}{RGB}{203, 216, 240}
definecolor{arrb}{RGB}{97, 128, 183}
definecolor{arrc}{RGB}{71, 95, 139}
definecolor{nodet}{RGB}{97, 127, 180}
begin{document}
begin{tikzpicture}[box/.style={align=center,text width=2.7cm,
text=nodet,fill=myblue,rounded corners,draw=gray!50,
very thick,font=bfseriessffamily,minimum height=2cm,minimum width=2.7cm,blur shadow},
arr/.style={single arrow,fill=arrb,draw=arrc,thick,blur shadow,minimum height=2em,
single arrow head extend=3pt}]
matrix[matrix of nodes,nodes={box,anchor=center},column sep=1.2cm,row sep=1.2cm] (mat) {
 {Combinatorial \  Problem}
 &
 {Boolean \  Expression(s)}
 &
 {Conjuctive \  Normal Forms}
 \
 {Problem \ Solution}
 &
 {Assignment of \ Variable(s)}
 &
 {SAT \ Solvers}
 \
};

path foreach X [count=Y] in {2,3}
 {(mat-1-Y) -- (mat-1-X) node [midway,sloped,arr] {}
  (mat-2-Y) -- (mat-2-X) node [midway,sloped,arr,shape border rotate=180] {}};
path (mat-1-3) -- (mat-2-3) node [midway,sloped,arr] {};
end{tikzpicture}
end{document}