27.5 years = 330 months to fully depreciate

$169,000 / 330 = $512.12 per month for depreciation

Rental started in Dec, so half month depreciation = $256.06

30 days/365days = 8.22% business use

$256.06  * 8.22% = $21.05 

When I enter your data, I get depreciation = $21