4. The Wilson Company’s marketing manager has determined that the price elasticity of demand for its product equals −2.2. According to studies she carried out, the relationship between the amount spent by the firm on advertising and its sales is as follows: Advertising Expenditure Sales $100,000 $200,000 $300,000 $400,000 0 $1.0 million $1.3 million $1.5 million $1.6 million a) If the Wilson Company spends $200,000 on advertising, what is the marginal revenue from an extra dollar of advertising?