Anabelle, a retailer of tack and Western apparel, earns an average contribution margin of 35 percent on its sales volume. Recently, the advertising manager of a local "country" radio station offered to run numerous radio advertisements for Anabelle at a monthly cost of $2,600. Compute the amount by which the proposed radio advertising campaign must increase Anabelle's monthly sales volume to: a. Pay for itself. b. Increase operating income by $1,000 per month. (Round computations to the nearest dollar.)