For this case we have by definition, that the equation of a line in the slope-intersection form is given by:

Where:
m: It's the slope
b: It is the cutoff point with the y axis
We need two points through which the line passes to find the slope:

We found the slope:

So, the equation is of the form:

We substitute a point to find "b":

Finally, the equation is:

Answer:
Option C
Range = max-min= 150-119 = 31
Y-2 = m (x-6), where m = (2-4)/(6-2) = -2/4 = -1/2
y-2 = 1/2 (x-6)
Not enough information- the coupon will only be worth 24% after tax though.