7 copies of "Youth Science" stacked up, 42 mm high. If another 21 copies of the same "Youth Science" are added and stacked together, how many millimeters will be the height?
7本《少年科学》摞起来，高42毫米．如果又增加21本同样的《少年科学》，一起摞起来，高多少毫米？
<gadget id="calculator">42 / 7</gadget>
<output>6</output>

<gadget id="calculator">6 * 21</gadget>
<output>126</output>

<result>126</result>