Notice for ordinary resolution with special notice

Hi Really sorry again as no doubt a repeat question but one I’m stuck on. Opentuition mock exam question bank “When a public company wishes to pass an ordinary resolution with special notice at an “other general meeting” how many days notice should be given?” Answer = 21 I selected 28 due to it being cemented in my head as the notice required for a special resolution but I seem to remember the 21 day thing but more where the company was providing the details of the auditor terms for resignation or something like that (they effectively had up to week to make their preparations) but this was also at the agm. Can you briefly explain the answer at all? P.s. thanks again - I’ve truly gone from guessing my way through and understanding hardly anything to feeling I have a good grasp of the subject. Your continued support is appreciated beyond anything I can express. With open tuitions approach I feel I actually understand the reasoning behind the subject and am working towards becoming an accountant rather than memorising answers for the test.