A system with a First In First Out page replacement algorithm can store 3 pages in memory at any given time.

The diagram below illustrates the process, three time points have already been completed:

Complete the remaining pages with the incoming pages. Answer which pages are stored in the locations denoted "a?" and "b?". Write down your answer as a two digit response, e.g. if the pages were 8 and 9, write down 89 without spaces, commas or other symbols