Here’s my solution (it’s the one from the book):
And here’s the link:
http://www.lodev.org/jstumble/?board=11llllr0r1eelllier1lflrfrerflereereereeleeree
Description: Think of the left 3 bits as one register and the right 2 bits as another register. They both are set up to count down. The left register starts with a value of 5 (1 + 4 = 5) so that the 6th ball heads over to the right flipper. When it does, the right register starts counting down from 3. It counts out 3 red balls and the 4th is caught in the interceptor.