1. Yes, there is an association between the variables. This is because as the value of x or the number of buses per hour increases, the number of complaints decrease.
2. Yes, we have a negative slope here, A negative slope means that two variables are negatively related; that is, when x increases, y decreases, and when x decreases, y increases. Graphically, a negative slope means that as the line on the line graph moves from left to right, the line falls.
3. The equation of the regression line is y = a + bx  where b is the slope of the line and a is the y-intercept. We calculate the slope of the line between two points (0,60) and (5,40) by using the slope formula \frac{y_{2}-y_{1}}{x_{2}-x_{1}}. Plugging in x_{1} = 0, y_{1}=60, x_{2}= 5, y_{2}=40, we get the slope as \frac{40-60}{5-0} = \frac{-20}{5} = -4/ The y-intercept is 60.

          So plugging in these values in our equation of line we get the equation as y = -4x + 60.

Skills you may want to recall:

What is a negative slope

https://courses.lumenlearning.com/suny-microeconomics/chapter/reading-interpreting-slope/#:~:text=A%20negative%20slope%20means%20that,to%20right%2C%20the%20line%20falls.

What is the equation of a regression line

http://www.stat.yale.edu/Courses/1997-98/101/linreg.htm#:~:text=A%20linear%20regression%20line%20has,y%20when%20x%20%3D%200).