To copy a manuscript, it takes 12 hours for A to copy alone, and 15 hours for B to copy. The two of them copy together at the same time. When the copy is finished, A has copied 1800 characters more than B. How many words are in this manuscript?
抄写一份稿件，单独抄甲用12小时，乙要15小时，两人同时合抄，抄完时甲比乙多抄1800个字，这份稿件有多少字？
<gadget id="calculator">5 + 4</gadget>
<output>9</output>

<gadget id="calculator">5 / 9</gadget>
<output>5/9 = around 0.555556</output>

<gadget id="calculator">4 / 9</gadget>
<output>4/9 = around 0.444444</output>

<gadget id="calculator">(5/9) - (4/9)</gadget>
<output>1/9 = around 0.111111</output>

<gadget id="calculator">1_800 / (1/9)</gadget>
<output>16_200</output>

<result>16_200</result>