It is known that the sum of the lengths of the sides of a cube is 84 cm, what is the area of one of its faces?
已知一个正方体的棱长总和是84cm，则它的一个面的面积是多少？
<gadget id="calculator">84 / 12</gadget>
<output>7</output>

<gadget id="calculator">7 * 7</gadget>
<output>49</output>

<result>49</result>