The part labelled 'x' is the unlabelled side.
[tex]\begin{gathered} 14ft=14ft\text{ ( opposite side of a rectangle are equal)} \\ \text{Then, 20-14=6ft} \end{gathered}[/tex][tex]\begin{gathered} To\text{ find x, we have:} \\ x^2=8^2+6^2 \\ x^2=64+36 \\ x^2=100 \\ x=\sqrt[]{100} \\ x=10ft \end{gathered}[/tex]
Hence, the length of the unlabelled side is 10ft, which is Option A
