How long does the servicer have to acknowledge a borrower’s complaint in writing?

According to Section 6 of RESPA, borrowers who have a problem with the servicing of their loan (including escrow account questions), should contact their loan servicer in writing, describing the nature of their complaint. The servicer must acknowledge the complaint in writing within 20 business days of receipt of the complaint.

Question: How long does the servicer have to acknowledge a borrower’s complaint in writing?

Answer: 20 business days