Persons engaged in any business listed in Section 8-2-6(1) who are subject to an annual license tax shall be exempt from one-half (1/2) of the license tax set out therein if gross income or gross revenue, whichever is greater, derived from the business licensed does not exceed four thousand dollars ($4,000.00) during the calendar year immediately preceding the year for which the tax is collected. The licensee shall have the burden of applying for the exemption and of establishing the level of gross income or gross revenue, whichever is greater, derived during that year, on forms prescribed by the Town Clerk.