REO Speedwagon (originally styled as R.E.O. Speedwagon) is an American rock band from Champaign, Illinois. Formed in 1967, the band cultivated a following during the 1970s and achieved significant commercial success throughout the 1980s. Hi Infidelity (1980) contained four US Top 40 hits and is the group's best-selling album, with over ten million copies sold. Over the course of its career, the band has sold more than 40 million records and has charted thirteen Top 40 hits, including the number ones "

The stage was now set for the height of the band's popularity. On November 21, 1980, REO Speedwagon released Hi Infidelity, which represented a change in sound, going from hard rock to more pop-oriented material. Hi Infidelity spawned four hit singles written by Richrath and Cronin, including the chart-topping "Keep On Loving You" (Cronin), plus "Take It on the Run" (#5) (Richrath), "In Your Letter" (#20) (Richrath), and "Don't Let Him Go" (#24) (Cronin), and remained on the charts for 65 weeks, 32 of which were spent in the top ten, including 15 weeks atop the Billboard 200. Hi Infidelity sold over 10 million copies and set the bar for rock bands across the country.  The band's follow-up album, Good Trouble, was released in 1982. Although it was not as successful as its predecessor, the album performed moderately well commercially, featuring the hit singles "Keep the Fire Burnin'" (U.S. #7), "Sweet Time" (U.S. #26) and the Album Rock chart hit "The Key."  The band came storming back two years later with Wheels Are Turnin', an album that included the #1 hit single "Can't Fight This Feeling" plus three more hits: "I Do' Wanna Know" (U.S. #29), "One Lonely Night" (U.S. #19), and "Live Every Moment" (U.S. #34).  REO Speedwagon toured the US in 1985, including a sold-out concert in Madison, Wisconsin in May. On July 13, on the way to a show in Milwaukee, the band made a stop in Philadelphia to play at the US leg of Live Aid, which broke a record for number of viewers. They performed "Can't Fight This Feeling" and "Roll With the Changes," which featured members of the Beach Boys, the band members' families, and Paul Shaffer on stage for backing vocals.  1987's Life as We Know It saw a decline in sales, but still managed to provide the band with the top-20 hits "That Ain't Love" (U.S. #16) and "In My Dreams" (U.S. #19). The Hits (1988) is a compilation album from REO Speedwagon. It contains new tracks "Here With Me" and "I Don't Want to Lose You." "Here with Me" cracked the top 20 on the Billboard Hot 100 and the top ten on the Adult Contemporary chart. They were the last songs recorded with Gary Richrath and Alan GratzerAnswer this question using a quote from the following article:

What was REO's biggest selling hit?
the #1 hit single "Can't Fight This Feeling"