The flower bed is shown below:
To find the remaining lenght of the flower bed (which we named c) we can use the pythagorean theorem:

where a and b are the legs of the triangle, in this case both legs are equal to 6, then we have;
![\begin{gathered} c^2=6^2+6^2 \\ c^2=36+36 \\ c^2=72 \\ c=\sqrt[]{72} \\ c=8.5 \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/z4u2kaul1z9xp3iot155xnr54x4lep2mvc.png)
Therefore the remaining length is 8.5 ft.