Hi, could somebody break down the factorization step por favor? (13!12!) + (13!14!) = (13!12!)(1 + 14*13) Sure!! But please make sure you have a clear concept on factorials. See my previous post (for Quick look) and refer a book. (13!12!) + (13!14!) = (13!12!) + (13! 14! ) Just concentrate on what ...