Snack bars, luncheonette, beauty parlor, bookshop, newsstand and banks, provided that such use(s) shall not exceed 20,000 square feet of floor area or occupy more than 25% of the total floor area of the principal structure in which located, whichever is the lesser; that no one use shall occupy more than 10,000 square feet of floor area; and that such uses shall be located only on the ground level of the principal structure and that entrance and exit, excluding emergency doorway to such uses, shall be from doorways to an interior common hallway of the principal building.