ANSWER

49 minutes

100 feet for 13 minutes -> Group E
Group E on the surface for 2:20 ->C
Group C at 70 feet  max time -> 25 (so 18 minutes is o.k.).  Residual Nitrogen time is 15 minutes.  Add RNT (residual nitrogen time) to ABT (actual bottom time) of 18 to get 33 minutes.

70 feet for 33 minutes ->G
G out for 3 hours ->C;    C at 50 feet can stay 49 minutes (21 minutes RNT)

 

Text Box: 13 min Text Box: 18 min Text Box: 49 min