please help explain the first part and help solve the last part

Nov.-Credit sales, collection of Nov. sales in Jan. Dec.Credit sales, collection of Dec. sales in Jan. Dec.Credit sales, collection of Dec. sales in Feb. Jan.Credit sales, collection of Jan. sales in Jan. Jan.Credit sales, collection of Jan. sales in Feb. Jan.Credit sales, collection of Jan. sales in Mar. Feb.Credit sales, collection of Feb. sales in Feb. Feb.Credit sales, collection of Feb. sales in Mar. JH Nov.-Credit sales, collection of Nov. sales in Jan. Dec.Credit sales, collection of Dec. sales in Jan. Dec.Credit sales, collection of Dec. sales in Feb. Jan.Credit sales, collection of Jan. sales in Jan. Jan.Credit sales, collection of Jan. sales in Feb. Jan.Credit sales, collection of Jan. sales in Mar. Feb.Credit sales, collection of Feb. sales in Feb. Feb.Credit sales, collection of Feb. sales in Mar. JH