The expression: 553.7x + 27,966
Can be used to approximate the average annual salary in dollars of public school teacher in the year 1985 + x
What was the average teacher's salary in 1993?
1993- 1985= 8 years
553.7x 8 + 27966
4429.6 + 27966
$32,395.60

In which year will the average salary reach $45,000?
45000 = 553.7x + 27966 the subtract 27966.
17034 = 553.7x by 553.7
x = 30.76 years
Help me explain answer into words.

Is that a question asked to you or is that a question you were wondering?

Because I really doubt a book/teacher would ask you to explain why the expression gives those results.

x = 30.76 years
Help me explain answer into words.

So far so good. They want the year when average salaries = $45K, so add 30.76 to 1985 and you get 2015.76. This means that sometime in the year2015 the median salary is expected to hit $45K.