a) XCo is not subject to tax in State X because it has no sales in that State, and it is not taxable in State Y because of the protection provided by PL 86-272. b) XCo is taxable on all of its income by State X because of the operation of the throwback rule, and it is not taxable in State Y because of the protection provided by PL 86-272. c) XCo is taxable on all of its income by State X because of the operation of the throwback rule, and it is taxable in State Y on 20 percent of its income. d) XCo is not taxable at all in State X because it has no sales in that State, and it is taxable in State Y on 20 percent of its income. e) XCo is taxable in State X on 80 percent of its income because of the operation of the throwback rule, and it is taxable in State Y on the remaining 20 percent of its income