A classroom with a flat top is 8.5 meters long, 6 meters wide and 4.2 meters high. The classroom doors, windows and blackboards have a total area of 35.8 square meters. How many square meters will be painted on the top and four walls of the classroom?
一间平顶教室，长是8.5米，宽6米，高4.2米．教室的门窗和黑板的面积一共有35.8平方米．要粉刷教室的顶面和四面墙壁，粉刷的面积有多少平方米？
<gadget id="calculator">8.5 * 4.2</gadget>
<output>35.7</output>

<gadget id="calculator">6 * 4.2</gadget>
<output>25.2</output>

<gadget id="calculator">35.7 + 25.2</gadget>
<output>60.9</output>

<gadget id="calculator">2 * 60.9</gadget>
<output>121.8</output>

<gadget id="calculator">8.5 * 6</gadget>
<output>51</output>

<gadget id="calculator">51 - 35.8</gadget>
<output>15.2</output>

<gadget id="calculator">121.8 + 15.2</gadget>
<output>137</output>

<result>137</result>