The function P(x) = -1.25x +975a - 3500 gives the profit when a units of a certain product are sold. Find a) the profit when 90 units are sold dollars b) the average profit per unit when 90 units are sold dollars per unit c) the rate that profit is changing when exactly 90 units are sold dollars per unit d) the rate that profit changes on average when the number of units sold rises from 90 to 180. dollars per unit e) The number of units sold when profit stops increasing and starts decreasing. (Round to the nearest whole number if necessary.) units