Umbrella Corporation sold 700 tractors on January 1, 2006. Umbrella paid $80,000 and $60,000, respectively, during 2006 and 2007 servicing the 3-year warranties that accompany the tractors. The warranties are not an integral part of the sale. Of the total revenues of $4.5 million derived from tractor sales, $450,000 were attributable to the sale of warranties. Umbrella estimated the total cost of servicing the 3-year warranties to be $320,000 as of December 31, 2006 and revised that estimate to $140,000 on December 31, 2007. Umbrella records warranty revenue prorata over the term of servicing the warranties. What is the balance of unearned warranty revenue as of December 31, 2007?