On a parallelogram, the diagonals intersect at their midpoints. Then, each segment of a diagonal must have the same length. Then:
[tex]\begin{gathered} c+5=11 \\ d+4=14 \end{gathered}[/tex]
Solve for each variable from the corresponding equation:
[tex]\begin{gathered} c+5=11 \\ \Rightarrow c=11-5 \\ \therefore c=6 \end{gathered}[/tex][tex]\begin{gathered} d+4=14 \\ \Rightarrow d=14-4 \\ \therefore d=10 \end{gathered}[/tex]
