Which of the following equations best models the data plotted below? a. y = x + 4 b. y = 4x + 9 c. y = x + 18 d. y = 3x + 22

The key with these problems is to find which function has the closest y-intercept to the graph, and then try to figure out which one best approximates the slope. 
Here are our options:
A. y = x + 4 
B. y = 4x + 9 
C. y = x + 18 
D. y = 3x + 22
 
Which has the closest approximation of the y-intercept? 
The y-intercept is not directly given, but we can assume it is less than 10. 
That leaves us with A and B.

Which has the closest approximation of the slope? 
The graph, on average, seems to move up about 60 and over about 15. 
Slope = rise/run = 60/15 = 4. Although the slope isn't exactly 4, it's much closer to 4 than 1, which is slope for option A.

Therefore, the answer is 
B) y= 4x + 9