Sum column based on value of row sum

I have a list of people that are required to complete 16 units. I need to be able to sum up how many units each person has completed and how many units towards the goal of 16 are completed each month. Once a person earns 16 units the additional units are not counted in the monthly total. The sums listed in B2:B4 will be actual earned units and can be any total value. I tried using sumif but may Range and Sum_range were different sizes so the calculation isnt accurate. Any help would be appreciated.


Jan Feb Mar Apr May Jun
Sam 18 4 4 4 4 2
Bill 22 16 2 2 2
Mark 20 20
sum 20 8 8 8 4 2


Desired Results

Jan Feb Mar Apr May Jun
Sam 18 4 4 4 4 2
Bill 22 16 2 2 2
Mark 20 20
sum 20 4 4 20 0 0