What is the equation of the line of best fit for the following data? Round the slope and y-intercept of the line to three decimal places,
(4,3)(6,4)(8,9)(11,12)(13,17)

To graph y = 4, we make a horizontal line at 4 on the y axis. See image 1

Since it is a horizontal line on the y axis, no matter the input you have for x, the y value is going to be 4. So the points  (4, ) (5, )  =  (4, 4) (5,4 ) 

For your point ( , 2.59), this is saying y = 2.59 The missing value would be 0. our points are below assuming the information given is complete:
(4, ) (5, ) ( ,2.59)  =  (4, 4) (5,4 ) (0,2.59)