From 1st August to 31st October 2018, you get 35 refunds for the purchase of the HP 934 / 935XL pack of 4 high capacity black/cyan/magenta/yellow ink cartridges and a high capacity HP 934XL black ink cartridge (ref. 146159). See conditions here. Compatible ink cartridge for HP printers: Officejet 6812, 6815, 6820; Officejet Pro 6230 ePrinter, 6830, 6835