Question 725935
We are used to writing y as a function of x.
In this case, you need to write x as a (linear) function of p,
{{{x=mp+b}}} instead of {{{y=mx+b}}}
It is a linear function, so it graphs as a straight line.
That line passes through the points
(2.50,275), with coordinates p=2.50 and x=275, and
(2.00,350), with coordinates p=2.00 and x=350
 
To graph that line we have to change the labels on the axes to read p and x, instead of x and y
{{{drawing(300,300,-1,5,-100,900,
grid(1),
blue(circle(2,350,0.1)), blue(circle(2.5,275,0.1)),
blue(line(0,650,13/3,0)),locate(0.15,880,red(x)),
locate(4.5,-10,red(p)),red(line(4.7,-40,5,-40))
)}}}

To write the equation we can find the slope of the line passing through points (2.50,275) and (2.00,350) :
{{{m=(275-350)/(2.5-2)=-75/2.5=-150}}}
write the line in point slope form using point (2.350) as
{{{x-350=-150(p-2)}}}
and do a little algebra to transform that into the slope-intercept form
(or "solve for x").
{{{x-350=-150(p-2)}}} --> {{{x-350=-150p+300)}}} --> {{{highlight(x=-150p+650))}}}