A can complete the work in 16 days, working 6 hours a day.
Total hours A needs to complete the work:
16×6
=96 hours
B can complete the work in 12 days, working 9 hours a day.
Total hours B needs to complete the work:
12×9
=108 hours
A completes 961 of the work in 1 hour.
B completes 1081 of the work in 1 hour.
Together in 1 hour:
961+1081
Finding LCM of 96 and 108:
LCM =864
961=8649
1081=8648
8649+8648
=86417 of the work per hour
Working 8 hours a day together, work completed in 1 day:
8×86417
=864136
=10817 of the work
Total days needed to complete the work:
1÷10817
=1×17108
=17108 days
Therefore, they can complete the work in 17108 days.