Students in grades 4 and 5 collect tree species. Grade 4 collects 18.6 kilograms of species. Grade 4 collects 2.5 kilograms less than grade 5. How many kilograms of species are collected by the two grades?
四、五年级的学生采集树种，四年级采集树种18.6千克，四年级比五年级少采集2.5千克，两个年级一共采集多少千克树种？
<gadget id="calculator">18.6 + 2.5 + 18.6</gadget>
<output>39.7</output>

<result>39.7</result>