For this case we have the following function:

By definition, we have that a linear equation is of the form 
On the other hand, a quadratic equation is of the form
Then, the given equation is not a linear equation, it is not of the form 
Answer:
No, the equation is not linear. It is not of the form 
C would be your answer and here is how you would solve the problem.
Budget ≤ 1250 - 439
m = $811
The slope is roughly -6/1
I graphed the equation y= -6/1x+4 and it looked pretty similar to the graph on your screen I hope this helps :)