12. A 10-foot ladder is placed against a vertical wall. Suppose the bottom slides away from the wall at a constant rate of 4 feet per second. How fast is the top of the ladder sliding down the wall when the bottom is 8 feet from the wall? 13. Elasticity: Use the given Price-demand equation: p+0.02x = 200 a. Find f(p) Hint: solve for p first b. Find f'(p) c. Find the elasticity of demand, E(p) -pf'(p) f(p) d. What is the elasticity of demand when p = $9 and is it elastic, unit or inelastic? If E(p)> 1 It is elastic If 0 < E(p) < 1 It is inelastic If E(p) = 1 It is unit, no change