Adding lengths can require some odd conversions. Look at this example:
3 yd, 2 ft
+ 2 yd, 2 ft
-----------------
5 yd, 4 ft
We can't leave our answer as 5 yd, 4 ft. Since we can get a yard out
of 4 feet, we must convert 3 of the 4 feet to a yard, which gives us
the following answer:
6 yd, 1 ft
1 ft, 8 in
+ 1 ft, 7 in
------------------
2 ft, 15 in
We can't leave the answer as 2 ft, 15 in. We must convert the 15
inches to 1 ft 3 in and adjust our answer.
3 ft, 3 in
We could convert the 3 ft to 1 yd, but in this set of problems
we won't do that.