The business hours of the department store are from 9:00 am to 9:00 pm, how many hours are they open every day?
百货商店的营业时间是从上午9点到晚上9点，每天营业时间是多少小时．
<gadget id="calculator">21 - 9</gadget>
<output>12</output>

<result>12</result>