Final answer:
The length of the Mississippi-Arkansas border within the Area of Interest rectangle is not provided in the given question.
Step-by-step explanation:
The question lacks specific information about the length of the Mississippi-Arkansas border within the Area of Interest rectangle. Therefore, it is not possible to provide a numerical answer or percentage based on the data given.
To determine the length of the Mississippi River today and calculate the change in length, it is essential to have data on both the original length of the river and its current length. Without this information, the computation required to express the change as a percentage cannot be performed accurately.
In conclusion, the answer to this question is dependent on the availability of specific data regarding the length of the Mississippi-Arkansas border within the specified area, as well as the original and current lengths of the Mississippi River. The question's response requires numerical values for these lengths to calculate the percentage change accurately.