To find the percent error of a measurement, you need to compare the measured value to the true or accepted value. The formula for percent error is:
\[ \text{Percent Error} = \left( \frac{\text{Measured Value} - \text{True Value}}{\text{True Value}} \right) \times 100% \]
However, since you didn't provide a true or accepted value for the length of the rope, we can't calculate the percent error without that information.
If you have a true value for the length of the rope, please provide it so that we can calculate the percent error accurately! If not, the percent error cannot be determined.