Hope Primary School participated in the tree planting activity. The ratio of the number of trees planted in grades 4, 5, and 6 is 2:3:4. It is known that grade 6 planted 84 more trees than grade 4. How many trees will be planted in the fourth, fifth and sixth grades?
希望小学参加植树活动，四、五、六三个年级植树棵数的比是2：3：4，已知六年级比四年级多植树84棵．四、五、六年级共植树多少棵？
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