Herb and Randy are twin jazz musicians who perform as a trombone–saxophone duo. At the age of twenty, however, Randy got an irresistible offer to join a road trip to perform on a star 15 light-years away. To celebrate his bounteous luck, he bought a new vehicle for the trip—a deluxe space-coupe which could do 0.999c. Each of the twins promises to practice diligently, so they can reunite afterward. Randy’s gig goes so fabulously well, however, that he stays for a full 10 years before returning to Herb. After their reunion,

(a) How many years of practice will Randy have?

(b) How many years of practice will Herb have?