Passage: Mating occurs during the winter months. Once a female quoll has been impregnated, the folds on her abdomen convert into a pouch that opens at the back. The gestation period is 21 days. A baby quoll, or pup, is the size of a grain of rice. Up to 18 quolls are born in each litter, but only six survive the first two weeks. The survivors stay in their mother's pouch for eight weeks, suckling on one of the mother's six teats for milk. During the ninth week, the pups venture out of the pouch and onto the mother's back, where they remain for six weeks. Quolls reach maturity when they are one year old, and have a natural lifespan of between two and five years. A 2008 study of the pouches of tiger quolls reported the pouches' appearance were reliable indicators of the quolls' reproductive status: during the follicular phase, pouches were found to be red and have many secretions. After ovulation, pouches became deep and wet. Researchers can use this information to determine where a female quoll is in her ovarian cycle, which is anticipated to be helpful in breeding management.

Question: How long are the pups on their mother's back?
six weeks