$86.$ A $\backslash (512-\backslash$mathrm$\{$Hz$\}\backslash )$ tuning fork is struck and placed next to a tube with a movable piston, creating a tube with a variable length. The piston is slid down the pipe and resonance is reached when the piston is $115\mathrm{.}50$ cm from the open end. The next resonance is reached when the piston is