Assuming population increase has been linear here is the given data from the problem.
13090 - 12390 = 700 people
2010 - 2000 = 10 years
700 / 10 = 70 people per year
Based on the data, here is our equation
y = 70x + 13,090
b) 21,000 = 70x + 13,090
x = 113 years
113 + 2010 = Answer = year 2123
c) 0 = 70x + 13,090
x = -187
-187 + 2010 = Answer = year 1823