It is mentioned in the question that we are crossing Tail-Feather Length and Feather Color with short feather length and recessive feather color organisms.
P1: LlBb X llbb
Gametes: LB: Lb: lB: lb : lb
Offspring:
LlBb: 480
Llbb: 20
llBb: 20
llbb: 480
So as we see that perntal combinations are LlBb and llbb which means 480 + 480 organisms are just like parents while Llbb: 20 and llBb: 20 (20 +20=40) are recombinants.
Answer: It means that number of recombinants are 40.