Extrapolate values and sum
Try this one:

create table #test (
    date date,
    overdrawn tinyint
)

insert into #test values
    ('2018-09-20', 1),
    ('2018-09-21', 1),
    ('2018-09-24', 0),
    ('2018-09-25', 1),
    ('2018-09-26', 1)

select sum(
        case datepart(dw, date)
            when 6 then overdrawn * 3 --Friday
            else overdrawn
        end
    )
from #test


This solution is based off the fact that the overdrawn field can either be 0 or 1 only. You'll have to include additional conditions if that's not the case.