If a supplementary assessment number six is levied by the board, immediately upon the supplementary assessment number six becoming a lien upon the lands, the board shall rescind and cancel its then existing order and the board may order that thereafter the assessment number six and the supplementary assessment number six shall be paid in semiannual installments equal to not less than 3¹/₂ per cent of the principal amount of the assessment for each installment.

(Added by Stats. 1943, Ch. 369.)