The students participated in tree planting activities. The fourth grade planted 42 trees, and the sixth grade planted 18 fewer trees than the fourth grade. How many fewer trees were planted in the fourth grade than in the sixth grade?
同学们参加植树活动，四年级栽了42棵，六年级栽的棵树比四年级的3倍少18棵，四年级比六年级少栽多少棵？
<gadget id="calculator">42 * 3</gadget>
<output>126</output>

<gadget id="calculator">126 - 18 - 42</gadget>
<output>66</output>

<result>66</result>