The function P(x) = -3.75x² +975x - 4500 gives the profit when I units of a certain product are sold. Find a) the profit when 85 units are sold dollars b) the average profit per unit when 85 units are sold dollars per unit c) the rate that profit is changing when exactly 85 units are sold dollars per unit

According to Bartleby guidelines we are supposed to do the first three sub parts 

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Given profit function