The fourth and fifth grade students collected tree species, the fourth grade collected 18 kilograms, and the fifth grade collected 2.55 kilograms less than the fourth grade. How many kilograms were collected in the fourth and fifth grades?
四、五年级同学采集树种，四年级采集了18千克，五年级比四年级少采集2.55千克，四、五年级一共采集多少千克？
<gadget id="calculator">18 - 2.55</gadget>
<output>15.45</output>

<gadget id="calculator">15.45 + 18</gadget>
<output>33.45</output>

<result>33.45</result>