The answer is: 10
I hope it’s helps you :)
I have found a table that gives the population of a town for the years 2000 - 2009. I also graphed it as attached here. A you can see, the slope of the graph is 81.9. SInce the equation gives us y = 81.903x - 162164. Substitute 2013 to x and you will get a y = 2706.74 which is also equal to the population of the town in the year 2013.
It is an acute triangle because none of its angles are equal to (right) or above (obtuse) 90 degrees.