Do these analogous to the base ten methods you learned in 
elementary school.  Just remember how to count in base 9.
You count: 1,2,3,4,5,6,7,8,10,11,12,13,14,15,16,17,18,20.
Every time you get to 8, you skip to 10. For there is no
9 in base 9.  9 in base 9 is written just like ten is
written in base ten, as 10.

Start as you would in 2nd grade lol:

 4 1 8 0 2
-2 3 7 4 5
----------
          
You can't subtract 5 from 2, so you have to borrow. You can't 
borrow from the 0, so borrow 1 from the 8.  Scratch the 8 and
put a 7 above it.  Now you leave the 0 an 8, (not a 9). 
Why an 8? Think what you'd do if it were base ten.  You'd 
leave the 0 with a 9 (which is 1 less than ten).  So you leave 
the zero with 1 less than 9, or 8.  So you have this:

     7 8
 4 1 8 0¹2
-2 3 7 4 5
----------

Now you need to subtract 5 from 12.  Count it out on your fingers.

To subtract 12-5, count on your fingers from 5 (not including 5) to 12
(including 12), but skip from 8 to 10.  Like this. On your fingers count
6,7,8,10,11,12. That takes 6 fingers, so put 6 under the 5:

     7 8
 4 1 8 0¹2
-2 3 7 4 5
----------
         6


To subtract 8-4, count on your fingers from 4 (not including 4) to 8 
(including 8), but you won't have to skip from 8 to 10 this time 
because we only get to 8.  Like this. On your fingers count 5,6,7,8. 
That takes 4 fingers, so put 4 under the 4.
[That was exactly the same as in base 10, 8-4=4. Bases are all the 
same as long as you are in digits less than the base number.]  

     7 8
 4 1 8 0¹2
-2 3 7 4 5
----------
       4 6

The next is easy 7-7=0, so put a 0 under the 7. In any base 
when you subtract a digit from itself you always get 0.

     7 8
 4 1 8 0¹2
-2 3 7 4 5
----------
     0 4 6

Next, you can't subtract 3 from 1, so you have to borrow. You 
borrow 1 from the 4, scratch the 4 and put a 3 above it
 
 3   7 8
 4¹1 8 0¹2
-2 3 7 4 5
----------
     0 4 6

Now you need to subtract 3 from 11.  So you count on your
fingers. 

To subtract 11-3, count on your fingers from 3 (not including 5) 
to 11 (including 11), but skip from 8 to 10.  Like this. On your 
fingers count 4,5,6,7,8,10,11. That takes 7 fingers, so put 7 
under the 3:
 
 3   7 8
 4¹1 8 0¹2
-2 3 7 4 5
----------
   7 0 4 6

The rest is simply 3-2=1, because the digits are less than 9.
Put a 1 under the 2 and you're done.
 
 3   7 8
 4¹1 8 0¹2
-2 3 7 4 5
----------
 1 7 0 4 6

-------------------------------------------------

  2 0 1 1 2
 +1 1 0 2 1
 ----------

Here we skip all the way from 2 to 10, because 3
is written as 10.  2+1=3 but there is no 3 in base 
three. so we skip from 2 to 10.  We put 0 under
the 1 and carry 1 to the next column, like this:

        1
  2 0 1 1 2
 +1 1 0 2 1
 ----------
          0

Now you have to add 1+1+2. Count on your fingers:
1+1=2 but since you are at 2 (1 less than the base number)
you must skip up to 10 and count 10,11. So in base three
1+1+2=11, so you put 1 under the 2 and carry 1 to the
next column.

      1 1
  2 0 1 1 2
 +1 1 0 2 1
 ----------
        1 0

Now you have to add 1+1+0.  That's easy because we don't
have to skip to 10.  So 1+1+0=2 just as in base ten. So
we put a 2 under the 0, and there's nothing to carry.

      1 1
  2 0 1 1 2
 +1 1 0 2 1
 ----------
      2 1 0

The next is also easy. 0+1=1. Put a 1 under the 1 and
there's nothing to carry:

      1 1
  2 0 1 1 2
 +1 1 0 2 1
 ----------
    1 2 1 0

Finally we have 2+1.  That would be 3, but there is no
3 in base 3, so we skip to 10, which gives us an extra 
digit on the left:

      1 1
  2 0 1 1 2
 +1 1 0 2 1
 ----------
1 0 1 2 1 0

Edwin