The students participated in the tree planting labor, 142 people went to the fourth grade, and 128 people went to the third grade. How many people in the fourth grade should be sent to support the third grade, so that the number of people in the two grades participating in the labor force is the same.
同学们参加植树劳动，四年级去了142人，三年级去了128人．四年级应该派多少人去支援三年级，就能使两个年级参加劳动的人数一样多．
<gadget id="calculator">142 + 128</gadget>
<output>270</output>

<gadget id="calculator">270 / 2</gadget>
<output>135</output>

<gadget id="calculator">142 - 135</gadget>
<output>7</output>

<result>7</result>