A factory is actively carrying out tree planting activities. 45 people in the first workshop planted 315 trees in total; 42 people in the second workshop planted 8 trees on average. How many fewer trees were planted in the first workshop than in the second workshop?
某工厂积极开展植树活动．第一车间45人共植树315棵；第二车间42人，平均每人植树8棵．第一车间比第二车间少植树多少棵？
<gadget id="calculator">42 * 8</gadget>
<output>336</output>

<gadget id="calculator">336 - 315</gadget>
<output>21</output>

<result>21</result>