I have two circles that are congruent to each other one has a lenght of 8ft and the second is half of 8ft. What is the length of the second circle
Your question makes no sense.
To me congruent circles would be circles that have the same radius.
What do you mean by "one has a lenght of 8ft"
Is that supposed to be the circumference ?
If the second has a "length" of 4 ft, then it must be smaller, therefore they can't be "congruent"