B. Manischewitz Co. gave a suitor, National...

B. Manischewitz Co. gave a suitor, National Foods, until 5 p.m. Wednesday New York time to deliver its “best and final” offer; rival Levine, Tessler, Leichtman & Co. will then have one hour to try to top the bid . . . Great Western Financial Corp. has agreed to sell its six Spokane, Wash., retail banking branches to Washington Trust Bank of Spokane. Terms were not disclosed . . . The number of working oil and gas rigs increased by seven rigs last week to 817, marking the sixth straight weekly gain . . . Northwest Airlines lowered round-trip air fares to $152 for travel beginning later this week to and from most domestic destinations where it competes directly with Continental Airlines. The action was in response to this week’s Continental fare reduction . . . USAir will begin nonstop service between Los Angeles International Airport and Philadelphia beginning Sept. 15.