Design a group gymnastics performance formation, and want to form a 6-story hollow square formation. It is known that there are 360 people participating in the performance. How many people should be arranged on each side of the outermost layer?
设计一个团体操表演队形，想排成6层的中空方阵，已知参加表演的有360人，求最外层每边应安排多少人？
<gadget id="calculator">6 * 6 * 4</gadget>
<output>144</output>

<gadget id="calculator">144 + 360</gadget>
<output>504</output>

<gadget id="calculator">6 * 4</gadget>
<output>24</output>

<gadget id="calculator">504 / 24</gadget>
<output>21</output>

<result>21</result>