The poverty level income for a family of four was
$9287 in 1981. Due to inflation and other factors,
the poverty level income rose to approximately
$18,267 in 2001. (Source: U.S. Census Bureau)

a. Find a linear equation that approximates the
poverty level income y in year x (with x = 0
corresponding to 1981).

b. Use the equation of part a to estimate the
poverty level income in 1990 and 2005.