it is a simple procedure either you can. simply put any alphabet, for this example we will use B. all you do is, type B, 13 times, an then type B agai, 16 times. and count them all. so here we go

B1 B2 B3 B4 B5 B6 B7 B8 B9 B10 B11 B12 B13

now step two

B1 B2 B3 B4 B5 B6 B7 B8 B9 B10 B11 B12 B13 B14 B15 B16,

Now count the total number of B's.

we have.

13 B's on Top
and
16 B's Below.

Now

Again, Count B's. or Type all b's below, without numbering them.

B B B B B B B B B B B B B B B B B B B B B B B B B B B B B

Now, if you have counted all the B's you get 29 B's.

This is the simplest method of calculating.

Now, If you need another method that is called the break off system, but for this a little bit of brain is required, the above method was successfully experimented on lab animals.

Ok, Method 2.

13 + 16

break it up into smaller numbers that you can hold in your head like

10 + 3 + 10 + 6
now add BIG number's first

like, 10 + 10 so you get the answer 20

now add the smaller number's i.e 3 + 6 you get the answer 9

now add 20 + 9 and you get the answer 29.

Do you want a third method, or are the above two enough. :)