A licence code is composed of 3 letters and 3 numbers. The sum of the 3 numbers is 9. How many possible codes are there? Im really stuck with the requirement that the sum of the digits is 9. I tried making a table and concluded that there were 13 possible combinations of numbers that had the sum of 9, although i did it in a rush, so im not to confident with my result. How should i calculate the number of combinations of numbers that add to 9? Once i know how to do this, i think i should be alright in finishing the question. Thanks in advance. Dan.