Class 5 and Class 2 collected 21.4 kg of tree species, and Class 5 and Class 3 collected 3.7 kg less than Class 5 and Class 2. How many kg of tree species were collected by the two classes?
五2班采集树种21.4千克，五3班比五2班少采集3.7千克，两个班共采集树种多少千克？
<gadget id="calculator">21.4 - 3.7</gadget>
<output>17.7</output>

<gadget id="calculator">17.7 + 21.4</gadget>
<output>39.1</output>

<result>39.1</result>