6. In order to prevent Bald Qiang from stealing bananas, at least one of the bears, Big Bear and Little Bear, will patrol the forest. If Big Bear patrols alone, Bald Qiang can pick 8 bananas per minute; if Little Bear patrols alone, Bald Qiang can pick 10 bananas per minute; if both Big Bear and Little Bear patrol together, Bald Qiang can only pick 4 bananas per minute. Now, Bald Qiang picked a total of 88 bananas in 12 minutes. It is known that during the time Bald Qiang was stealing bananas, Big Bear's patrol time was twice that of Little Bear. How many minutes did Big Bear patrol? $\qquad$
$10$