The demand function for a certain make of inkjet cartridge i

The demand function for a certain make of ink-jet cartridge is the following where p is the unit price in dollars and x is the quantity demanded each week, measured in units of a thousand.
p= (-0.02x^2)-0.2x +6
Compute the elasticity of demand when x = 8. (Round your answer to two decimal places.)

at x= 8, p = 3.12 dp/dx = -0.04*x - 0.2 or, dp/dx = -0.52 elasticity of demand = p/x * (dx/dp) = (3.12/8) * (1/-0.52) = - 0.75