I have roadway segments that have been rated 1-5. Each segment has a
different length. I want to calculate the average rating for the total
length. How do I do that and make it a function of length. example:
road A has a rating of 5 and is 3 miles long
road B has a rating of 3 and is 1 miles long
road C has a rating of 2 and is 2 miles long

What is the average rating?