An office with a length of 8 meters, a width of 6 meters, and a height of 2.8 meters needs to be painted on the four walls. It is known that the doors and windows are 42 square meters in total. How big is the area that needs to be painted?
一间长8米、宽6米、高2.8米的办公室，需要粉刷四壁，已知门窗共42平方米，需要粉刷的面积有多大？
<gadget id="calculator">8 * 2.8</gadget>
<output>22.4</output>

<gadget id="calculator">6 * 2.8</gadget>
<output>16.8</output>

<gadget id="calculator">22.4 + 16.8</gadget>
<output>39.2</output>

<gadget id="calculator">39.2 * 2</gadget>
<output>78.4</output>

<gadget id="calculator">78.4 - 42</gadget>
<output>36.4</output>

<result>36.4</result>