You've read about the Oort cloud, and about how the orbits of some objects within it are perturbed by gravity into ellipses that pass close to the sun at one end. Here's a way to figure this out using what you know from reading the Comet's Tale.
Scientists sometimes make some assumptions to simplify their work.
Look for the assumptions here. Look for underlined words in the Comet's Tale glossary. One year is 31,536,000 seconds. Compare this to the time it takes light to cross the Oort Cloud. First, figure out how many AU the comet would go if it traveled at light speed.