Question 723944
Look just at finding the linear model.  Two points.  Use price per gallon for x and gallons per hour sold for y.  Your two points (x,y) are (2.15,1600) and (2.55,800).  


Slope {{{m=(1600-800)/(0.15-0.55)}}}
{{{m=800/0.40}}}
{{{m=2000}}}


Using point-slope form for a line, and the lower-y point, 
{{{y-800=2000(x-2.55)}}}
{{{highlight(y=2000(x-2.55)+800)}}}