How do you solve for x when x squared = 9?

The customer price index(cpi), which measures the cost of a typical package of customer goods,was 208.8 in 2011 and 244.1 in 2016.let x=11 corresponding to the year 2011 an estimate to cpi into 2013 and 2014. assume that the data can be modeled by a straight line and the trend to continue idenfinitely.use data points to find such a line and then estimate the requested quantities

Pls never taught i’m really confused and i rlly need

What is the slope of the line that contains the points (-5, 6) and (14. - 7)?