Two students typed a manuscript together and completed it in 3 days. A typed 4,000 words a day, and B typed 4,200 words a day. How many words are there in this manuscript? (answer in two ways)
两个同学共同打一份稿件，3天完成．甲每天打4000字，乙每天打4200字，这份稿件共多少字？(用两种方法解答)
<gadget id="calculator">4_000 * 3</gadget>
<output>12_000</output>

<gadget id="calculator">4_200 * 3</gadget>
<output>12_600</output>

<gadget id="calculator">12_000 + 12_600</gadget>
<output>24_600</output>

<result>24_600</result>