Hope Primary School participated in the tree planting activity, and assigned the tasks to grades four, five, and six according to the ratio of 2:3:4. It is known that grades six planted 84 more trees than grade four. How many trees were planted in total for the three grades in this task?
希望小学参加植树活动，把任务按2：3：4分配给四、五、六三个年级，已知六年级比四年级多植树84棵，这次任务三个年级共植树多少棵？
<gadget id="calculator">4 - 2</gadget>
<output>2</output>

<gadget id="calculator">84 / 2</gadget>
<output>42</output>

<gadget id="calculator">2 + 3 + 4</gadget>
<output>9</output>

<gadget id="calculator">42 * 9</gadget>
<output>378</output>

<result>378</result>