With A, chain 18.
Row 1: Double crochet in 4th chain from hook and in each chain across. The beginning chain 3 counts as one double crochet, so at the end of Row 1 you will have 16 stitches.
Row 2: Chain 3 (counts as first double crochet), turn, double crochet in each stitch across and in the top of the chain 3 - 16 stitches at end of row.
With A, repeat Row 2 until the piece measures about 5 1/2 in. (14 cm) from beginning.
Fasten off A.
Join B with a slip stitch and repeat Row 2 until B section is about 5 1/2 in. (14 cm).
Continue to repeat Row 2, alternating A and B every 5 1/2 in. (14 cm), until Scarf measures about 40 in. (101.5 cm) from beginning.
Weave in ends.