Biweekly Payroll Calculation

I have a biweekly payroll problem for calculating unpaid time off/sick:
Salary $36,000
Biweekly of $1500
Hourly $17.31

The pay period was from 03/25/2015 to 4/06/2015 = to 12 days’ pay period at 96hrs
In this pay period this person take an unpaid day off:

1 day off $1500-(8*$17.31) =1361.52
2 days off
3 days off
Up to

11 days off $1500-(88*$17.31) = -$23.28 now this is a problem with this formulas it seem like the person is underpay how do I solve this problem.

Theoretically 96hrs *$17.31 = $1661.76 but this person is a salary employee so $1500 is the biweekly paycheck.

Any suggestion or advices great appreciated.

Thank You