A firm's value added refers to the dollar value of OA a firm's sales revenue minus the firm's purchases of intermediate products from other firms OB. a firm's sales revenue minus the firm's profits Oc. a firm's total sales revenue. O.D. the intermediate products a firm buys from other producers. Suppose U.S. drivers purchased $60 billion of ExxonMobil-produced gasoline during a recent year, with one-half purchased directly from ExxonMobil-owned gas stations and one-half from independent (or third-party) gas stations. Suppose further that ExxonMobil purchased the oil (which it refined into gasoline) from foreign producers for $22 billion and that it receives 60 percent of the sales revenue that independent stations generate from selling ExxonMobil gasoline. In this case, the value added by ExxonMobil to US. GDP is $ billion. (Enter your response as an integer.)