Final answer:
The Mortgage Company must provide Donald with a written explanation of their decision to reject his loan application within 30 days of receiving the application, which means by September 4.
Step-by-step explanation:
Under the Equal Credit Opportunity Act (ECOA), a creditor must notify an applicant of its decision on the application within 30 days after receiving it. If an application is denied, the creditor must provide the applicant with a written statement of reasons for the denial or notice of the applicant's right to obtain such a statement within 30 days after receiving the application. Therefore, since Donald's loan application was rejected on August 5, the Mortgage Company must send him a written explanation by September 4, assuming non-leap year. It is important to note that the 30-day period starts from the date of the application receipt, not the date of the application decision.