In order to welcome the first-year freshmen at the beginning of the school term in Sanxin Junior High School, the roofs and 4 walls of the 20 classrooms in the first-year junior high school were painted. Each classroom is 10 meters long, 8 meters wide and 3.5 meters high. The doors, windows and blackboards of each classroom are 20 square meters in total. What is the volume of each classroom? How many square meters is the painted part?
三鑫初中部开学初为了欢迎初一新生，对初一年级的20间教室的屋顶和4面墙壁都粉刷了一遍．每间教室从里面量长10米，宽8米，高3.5米．每间教室的门窗和黑板一共20平方米，每间教室的容积是多大？粉刷的部分一共有多少平方米？
<gadget id="calculator">126 - 20</gadget>
<output>106</output>

<gadget id="calculator">80 + 106</gadget>
<output>186</output>

<gadget id="calculator">186 * 20</gadget>
<output>3_720</output>

<result>3_720</result>