Answer: Use the formula: 2(pi)(r + 1) - 2(pi)r
In your problem, you didn't give any measurements to use, so we can't determine an exact answer. However, the given formula above would work.
The first term calculates the extended length of rope. The second term calculates the original length of rope. All you need to do is subtract them.
Online, you can find the radius of the Earth if you need an exact value. 3,959 miles