Please show all work including algebra. Thank you.

12 Find the value of dy when 2 = 3 and do = ool for fcX ) = 5x- 3 . compare this with the value of by when x = 3 and AM = 0. 01 13 A commodity has a demand function modeled by P = 280 - 0.4x and a total cost function modeled by C = Sox + 120, where a is the number of units . a what price yields a maximum profit? Find the average cost per unit when x = 50 and X = 650 . () Determine when the demand is elastic , inelastic , and of unit elasticity . ( d) use differentials to approximate the change in revenue in sales increase from 210 units to 220 units . compare this with the actual change in revenue