The third grade students collect 30 kilograms of tree species, the fourth grade students collect 6 bags of tree species, each bag is 7 kg, how many kilograms of tree species are collected by the fourth grade?
三年级同学收集树种30千克，四年级同学收集树种6袋，每袋7千克，四年级收集树种多少千克？
<gadget id="calculator">6 * 7</gadget>
<output>42</output>

<result>42</result>