A building has five units, each unit has 21 floors, and each floor houses 3 households. How many households are there in this building?
一幢楼有五个单元，每个单元有21层，每层住着3户．这幢楼一共有多少户？
<gadget id="calculator">3 * 21 * 5</gadget>
<output>315</output>

<result>315</result>