I have a client that needs help and I know the sumif function would work
here, but I must be doing something wrong. She has one column with a letter
from A to G in it. In the other column is a number that varies. She wants to
take, for example, all the cells with a B and add up the numbers in the next
column for her total and do this for each letter.

D 12
D 6
D 30
D 6
D 6
D 18
D 12
E 12
E 6
E 6
E 6
E 6
E 6
E 30
E 0
E 24

Here are is a small portion of the sheet. Someone suggested that I use this
command =SUMIF(R5:R256,1,M5:M256) where R5:R256 has the letters and M5:M256
contain the values to add. I know this formula cannot be write because how
does it know what letter to look for, but I don't know how to fix it. Any
suggestions?