Two groups of students are going to plant trees. The number of students in the first group is three times that of the second group, and the number of students in the second group is 40 fewer than the three times of the first group. How many students are there in the voluntary tree planting?
两组同学去植树，第一组同学人数是第二组人数的3倍，而笫二组同学人数比第一组的3倍少40人，求参加义务植树的同学共有多少人？
<gadget id="calculator">3 * 3</gadget>
<output>9</output>

<gadget id="calculator">9 - 1</gadget>
<output>8</output>

<gadget id="calculator">40 / 8</gadget>
<output>5</output>

<gadget id="calculator">5 * 3</gadget>
<output>15</output>

<gadget id="calculator">15 + 5</gadget>
<output>20</output>

<result>20</result>