Hi there, PG-545 is the cartridge number. Does your printer already have the PG-545 ink cartridge inside? if it does, and you'd like to replace it, you can find the new cartridge here:
https://www.tonergiant.co.uk/product/Canon-PG-545-Black-Ink-Cartridge-8287B001-20470/.
If you want to find all the cartridges that go in your printer, the printer will have a specific model number. MG3000 is the series number but I need the exact model number to be able to check which are the correct inks for you. For example, the MG3100 and MG3050 are both MG3000 series but use different ink cartridges so I want to make sure I don't give you the incorrect ones.