Пре­об­ра­зуй­те, если это не­об­хо­ди­мо, слово BE так, чтобы оно грам­ма­ти­че­ски со­от­вет­ство­ва­ло со­дер­жа­нию тек­ста.

When the class was over, Heather sprinted to the bookstore, grabbed a copy and rushed to the cashier. The cashier saw Heather and began ringing the bell for assistance, a look of panic on her face. "How many ___________ there behind you?" she demanded.