What formula to use to pick frequent 4 digits compared between 2 cells/table range

G'day 2every1

im jason, from malaysia, i need your guidance for a simple formula i dont know how to use, coz i have basic in excel 2003.
1.What are the formula/s involved to identify 2/3/4 digit in a range of number in a cell that frequent compared to another cell/table
eg
table1 table2
5674 22346571 in this table we can identify 4digit
2224 11674821 ie in comparison to table 1 and 2
3169 75883242 5674 is frequently observed in table2
4474 71657473. in line 1-4657 and line 4-6574.
While for 3 digit 224 is frequent In Table 1 line 2 vs Table 2 line 3
I need a solution to filter 4 digit or 3 digit like the example from a
range of 2 or more tables.

2. Is there any possibilities to restrict accessbility of a excel worksheet for a certain period of time. for eg. i allow my colleague to view the worksheet for only 3 days, after which the worksheet will expire or self-terminate or unaccessible?

hope to hear a favourable reply from you soon
thanks a million.