There are about 17 weeks of classes in this semester, 5 days a week, excluding holidays and 5 days off. About how many days are there classes in this semester?
本学期上课大约有17周，每周上课5天，除去节假日放假5天．这学期大约上课多少天？
<gadget id="calculator">5 * 17</gadget>
<output>85</output>

<gadget id="calculator">85 - 5</gadget>
<output>80</output>

<result>80</result>