Oh I see. When you convert each of the letters in the word "challenge" to its position in the alphabet, you get 3 8 1 12 12 5 14 7 5. Adding up all of these numbers gives 67. Doing the same for the words "fifty" and "five" gives 66 and 42 respectively. So, 67'66'42 is an encoding of the title of the challenge in this way.
'mushroomsteve' you have done it again. Congratulations for working out a tricky challenge. Your 9th 'Honorary Golden Medal' is on the way ........ Well done!