The formula for the distance between two points is
[tex]d=\sqrt[]{(x_2-x_1)^2+(y_2-y_1)^2}[/tex]So, in this case, you have
[tex]\begin{gathered} (x_1,y_1)=(4,5) \\ (x_2,y_2)=(0,2) \end{gathered}[/tex][tex]\begin{gathered} d=\sqrt[]{(0-4)^2+(2-5)^2} \\ d=\sqrt[]{(-4)^2+(-3)^2} \\ d=\sqrt[]{16+9} \\ d=\sqrt[]{25} \\ d=5 \end{gathered}[/tex]Therefore, the distance between points C and D is 5 units.