Aline passes through (4, 5) and (8, 9). which equation best represents the line?

Find the slope of the line that will go through point (4, 5) and (8, 9) first and then you can use the point-slope form to figure out the equation of the line. Since I am not sure what form of the equation they want, I will just provide you the point-slope form, standard form, and the slope-intercept form of the line. 

The slope can be calculated by subtracting the difference of the y-coordinates of the two points and then dividing it by the difference of the x-coordinates. 

(y_2 - y_1) / (x_2 - x_1) = slope
(9 - 5) / (8 - 4) = 4 / 4 = 1

The point-slope form is: y - y_1 = m(x - x_1)
Let's take the coordinate (4, 5) and use 4 for x_1 and 5 for y_1. 
y - 5 = 1(x - 4) 

The slope-intercept form is: y = mx + b
We can modify the point-slope form to look like the slope-intercept form. 
y - 5 = 1(x - 4) 
y = x - 4 + 5
y = x + 1

The standard form is: ax + by = c
We can modify the slope-intercept form to look like the standard form.
y = x + 1
y - x = 1
-x + y = 1

Point-slope form: y - 5 = 1(x - 4) 
Slope-intercept form: y = x + 1
Standard form: -x + y = 1