The third and fourth grade students collected tree species, the third grade collected 12.6kg, and the fourth grade collected 2.8kg more tree species than the third grade. How many kg did the two grades collect in total?
三、四年级的学生采集树种，三年级采集了12.6kg，四年级采集的树种比三年级多2.8kg．两个年级共采集了多少kg？
<gadget id="calculator">12.6 + 2.8 + 12.6</gadget>
<output>28</output>

<result>28</result>