Xiao Ming typed an 840-character composition manuscript, and he has already typed 168 characters. If he typed 42 words per minute, how many minutes would it take to finish typing?
小明打一份840个字的作文稿，已经打了168个字．如果他每分钟打42个字，还要几分钟才能打完？
<gadget id="calculator">840 - 168</gadget>
<output>672</output>

<gadget id="calculator">672 / 42</gadget>
<output>16</output>

<result>16</result>