Alex is a self-employed dentist who operates a qualifying office in his home. Alex has $180,000 gross income from his practice and $160,000 of expenses directly related to the business, i.e., non-home office expenses. Alex's allocable home office expenses for mortgage interest expenses and property taxes are $14,000 and other home office expenses are $9,000. What is Alex's total allowable home office deduction?

A) $9,000

B) $14,000

C) $20,000

D) $23,000