Router header length = 448 / 8 = 56 bytes
We know,
First 8 bytes are fixed( Next header(1 byte), Header Extension length(1 byte), Routingtype(1 byte), segments left(1 byte), Reserved(4 bytes)).
So 56 - 8 = 48 bytes are hop addresses.
Each address is 16 bytes.
So 48 / 16 = 3