Assume that in january 2013, the average house price in a particular area was $289,400. in january 2000, the average price was $206,300. what was the annual increase in selling price?

The problem is an arithmetic sequence with:
a₁ = 206,300
an = 208,400

n = 2013 - 2000
n = 13

To find the annual increase, use this following formula
an = a₁ + d(n - 1)
d represents the annual increase

Input the numbers
an = a₁ + d(n - 1)
289,400 = 206,300 + d(13 - 1)
289,400 = 206,300 + 12d
289,400 - 206,300 = 13d
83,100 = 12d
12d = 83,100
    d = 83,100/12
    d = 6,925

The annual increase is $6925