Hello, Thanks for all your help in the past. I have another problem i don't understand.

The problem text is:

A simplified code system for a computer network consists of code words using the numbers 0,1,2,3,... 7. That is the octal number system. A code word is valid if it contains an even number of 4's.

Sett up an equationfor the number of valid code words of length n.

The answer is supposed to be:

y_n - 6y_(n-1)=8^(n-1), n >= 1

y_0 = 1

The problem is i don't understand how they have arrived at this solution.

(English is not my native language, so i might have gotten some of the math words wrong).