Suppose the profit \(P\) (in dollars) of a certain item is given by \(P=1.25 x-850\), where \(x\) is the number of items sold.

a. Graph this profit relationship.

b. Interpret the value of \(P\) when \(x=0\).

c. The slope of this graph is called the marginal profit. Find the marginal profit, and give an interpretation.