First find how many planks there are:
8 sections x 12 planks per section = 96 total planks.
If 1 person can do 1 plank in 3 minutes, then 2 people can do 2 planks in 3 minutes.
96 planks ÷ 2 planks = 48 sections of 3 minutes.
48 x 3 = 144 minutes
144 ÷ 60 = 2 hours 24 minutes