Halloween H20: 20 Years Later

On October 29, 1998, Marion Chambers (Nancy Stephens), Dr. Sam Loomis' former colleague, returns to her home in Langdon, Illinois, to find it has been burglarized. After having her neighbor Jimmy (Joseph Gordon-Levitt) and his friend Tony call the police, Jimmy searches the house and finds nothing. While waiting for the police, Marion discovers a file is missing, the one on Laurie Strode (Jamie Lee Curtis), Michael Myers' sister. She also realizes that someone has been in her house and immediately rushes back over to Jimmy's house, where she finds him and Tony dead. Michael Myers (Chris Durand) appears, and kills Marion. Michael leaves the house with Laurie's file.
On Halloween, two days later, Laurie Strode awakens from a nightmare, having to be calmed by her son, John (Josh Hartnett). Since 1978, she has tried to get her life together with the hope that her older brother would never come after her again. She faked her death in a car accident, and then relocated to California under the assumed name "Keri Tate". She has a seemingly perfect life with John, her boyfriend Will (Adam Arkin), and a career as headmistress at Hillcrest Academy, a private boarding school where John attends. Unfortunately, Laurie is far from happy, as the tragic events from 1978 still haunt her.
While a woman and her daughter are using a bathroom at a rest stop, the two narrowly avoid Michael, who steals the woman's car. At the campus, the students leave for an overnight field trip at the Yosemite National Park. Later that evening, John and his friends are having an intimate Halloween party in the basement when John's friend, Charlie (Adam Hann-Byrd), is attacked and killed by Michael. When Charlie's girlfriend Sarah (Jodi Lyn O'Keefe) goes looking for him, she finds him dead in the kitchen dumbwaiter with a corkscrew embedded in his throat, and Michael appears. She manages to get into the dumbwaiter next to Charlie and just as she closes the door Michael stabs her in the leg. The dumbwaiter heads up a level and as Sarah gets out Michael slashes the rope, causing the dumbwaiter to fall onto Sarah's leg, savagely disfiguring it. As she attempts to crawl for help Michael stabs her to death.
John and his girlfriend Molly (Michelle Williams) go looking for their friends. They find Sarah's body hung in the pantry and are chased by Michael through the school grounds. At one point in the chase, John is stabbed in the leg by Michael. Just as Michael is about to get Molly and John, they are saved by Laurie and Will, who open the door for them just in time. Just as the door closes behind them, Laurie and Michael come face to face for the first time since their last encounter twenty years ago. Laurie and Will hide Molly and John and decide to try to kill Michael.
When Will sees a shape approaching from the far end of the hall, he takes Laurie's handgun and shoots at the shape five times. When they check the downed shape, they discover that it was actually the school's security guard, Ronny (LL Cool J). Michael then appears and stabs Will in the back, killing him. Laurie helps John and Molly escape but she tells them to go for help while she chooses to go back to the school with a fire ax. She finds Michael and attempts to kill him several times, and finally after stabbing him multiple times, he topples over a balcony. She approaches his body and pulls one of the knives out of his chest. She slowly raises the knife high above her head, but before she can deliver the final blow, Ronny suddenly appears, having survived the shooting, and grabs her. He restrains her from attacking Michael and drags her out of the cafeteria insisting that Michael is dead.
The police come and put Michael in a body bag, loading it into a coroner's van. Laurie grabs the ax from earlier and an officer's gun, and she steals the van. While driving away, Michael sits up and escapes the body bag. She slams on the brakes, throwing him through the windshield. She then tries to run him over and the vehicle tumbles down a cliff, pinning Michael between the van and a tree. Laurie recovers the axe and approaches him. She decapitates Michael, finally killing him. Police sirens are heard as Laurie exhales.

Question: How many years back did Laurie last encounter Michael ?
Answer: Laurie encountered Michael last twenty years ago .