In the United States, the average public school teacher currently earns an annual salary near $55,202. Reported national average salaries for the last six decades are listed below.

Year
National Average
Teachers’ Salary
1960
$4,995
1970
$8,626
1980
$15,970
1990
$31,367
2000
$41,807
2010
$55,202

Determine the average salary increase per year between the years 1980 and 1990.
$8,367.80
$1,539.70
$1,004.10
$2,566.20