Answer:
The last digit you multiplied by.
Explanation:
It's not that hard, but here you go :)
If you multiplied 12 by 11 you would get 2 as your last digit, because 2 is the last digit of 12. (12x11=132)
So for 123 by 11, following this pattern, 3 is the last digit of 123 so the answer must end in 3. (123x11=1353)
If you still don't get the pattern I'll give you a few more examples here:
If you multiply 1234 by 11 you would get a number ending in 4 because the last digit of 1234 is 4! (1234x11=13574)
So what would be the last digit of 12345?
Hope this was helpful!
(The answer was 5 btw)