Suppose a monopolist's profit is highest at price of $30 when its marginal cost is $10 (a 200% markup), what must be the elasticity of demand? Or equivalently, what elasticity of demand makes $30 the highest profit price? Use the markup equation we derived in class (if you don't remember that, then you can assume marginal cost is constant and ask how much would demand need to change to hold profits unchanged when price increases by 1 percent).