Line of best fit

Ms. Musto opened a new coffee shop.  She recorded the number of customers she served between opening and noon for the first 20 days of business.  Her results are shown on the graph.  Which line best fits the data?

A.)  y = 3x + 10
B.)  y = 2x + 20
C.)  y = 3x + 30
​D.)  y = x + 20

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Taking a close look at the imaginary line that would travel through the center of the points, one can conclude:
the y-intercept of the line is approximately 20  (definitely not 10 and 30, so answers A and C are out)

Also, if it is possible, try to identify the precise location of two points, and find the approximate slope of the line through those two points.  
For example, it appears (10,45) and (15,55) would be two of the points showing.

y2 - y1 
---------- = slope of the line   {slope formula}
x2 - x1

55 - 45
--------- = slope of the line   {substituted coordinates into slope formula}
15 - 10

10
----- = slope   {subtracted in numerator and denominator}
 5

slope = 2   {reduced}

Slope-intercept form is y = mx + b
m is the slope and b is the y-intercept

Substituting the slope and y-intercept into slope-intercept form, you get
y = 2x + 20   {substituted slope and y-intercept in}

B.)  y = 2x + 20

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