To solve this problem, recall the formula for the perimeter of a rectangle:
[tex]P=2width+2length.[/tex]Substituting the given data, you get:
[tex]346ft=2(77ft)+2length.[/tex]Solving for the length you get:
[tex]\begin{gathered} 346ft-2(77ft)=2length, \\ 192ft=2length, \\ length=\frac{192ft}{2}=96ft. \end{gathered}[/tex]