(a) The interest charged for mortgage loans obtained according to the provisions of section three of this article shall not exceed the monthly index of long-term United States government bond yields for the calendar month preceding the date the commitment for such loan is made: Provided, That in no event shall the interest rate be more than twelve percent per annum, nor less than ten percent per annum. For the purposes of this section, the monthly index of long-term United States government bond yields means the monthly unweighted average of the daily unweighted average of the closing bid yield quotations in the over-the-counter market for all outstanding United States treasury bond issues which mature twenty years or more from the date the index is calculated, but shall not include such bonds as are redeemable at par for payment of federal estate taxes.

(b) The Housing Development Fund may charge such points to the seller of the real estate covered by the first mortgage deed or deed of trust as are necessary to offset costs of making the loan, including, but not limited to, the costs of processing the loan application and the costs of interest charges incurred between the commitment date of the loan and the date the property is actually purchased: Provided, That such points charged shall not exceed two points and shall be charged to the seller: Provided, however , That the real estate broker shall, from his or her commission, pay an amount equal to one point. The seller shall furnish to the fund satisfactory proof that he or she has not within the two years preceding the contract of the sale offered the house to the buyer for less than the sale price provided in the contract or sale between them. The proceeds from such points paid by the seller and broker to the Housing Development Fund, less actual Housing Development Fund expenses up to one half of one point, and less an amount equal to the first year cost for mortgage insurance required by section three of this article, shall be transmitted to the state Board of Investments as provided in section ten of this article.