A poverty threshold represents the minimum annual household income for a family not to be considered poor. In 1995, the poverty threshold for a family of four with two children under the age of 18 years was $15,651. In 2005, the poverty threshold for a family of four with two children under the age of 18 years was $19854. Assuming poverty thresholds increase in a straight-line fashion, use the midpoint formula to estimate the poverty threshold of a family of four with two children under the age of 18 in 2000. The poverty threshold of a family of four with two children under the age of 18 in 2000 is $(answer here).