A Monopoly Produces X at a Marginal Cost of $20

A monopoly produces X at a marginal cost of $20 per unit and charges a price of $50 per unit.Determine the elasticity of demand at the profit-maximizing price of $50.

A) −0.5
B) −.6
C) .67
D) There is insufficient information to determine the monopoly's price elasticity of demand.