Plant trees in spring. The fifth grade planted 12 trees, and the sixth grade planted 16 trees. The number of trees planted in the whole school was three times the number of trees planted in the fifth and sixth grades. How many trees were planted in the whole school?
春季植树．五年级植树12棵，六年级植树16棵，全校植树的棵数是五、六年级植树棵数的3倍，全校共植树多少棵？
<gadget id="calculator">12 + 16</gadget>
<output>28</output>

<gadget id="calculator">28 * 3</gadget>
<output>84</output>

<result>84</result>