Answer:
Fill the 3 gallon jug first.
Pour the 3 gallons into the 5 gallon jug.
Fill the 3 gallon jug again.
Fill up the 5 gallon jug with the 3 gallon jug.
You will have 1 gallon remaining in the 3 gallon jug.
Pour out the 5 gallon jug.
Pour the remaining spiced cider from the 3 gallon jug to the 5 gallon jug.
Fill the 3 gallon jug again.
Pour into the 5 gallon jug.
You will have 4 gallons!