Well divide them. 2/3=0.666 repeated. So use a bar over the top of the third six.
From the given table, the points can be written as : (6,7.55) , (12,7.85), (18, 8.15) and (24, 8.45)
Slope 
m = 
m = 0.05
slope intercept form of line = 
We plug m = 0.05, x = 6 and y = 7.55 and find c.

c= 7.25
Required equation:
... Answer
Answer:
the correct answer is 4 and 21