The students performed queue training and formed a hollow phalanx with 4 floors, and there were 15 more people. If another layer is added to the hollow part of the phalanx, there will be 21 fewer people. How many students are there in total?
同学们进行队列训练，排成一个4层的空心方阵，还多15人．如果在方阵的空心部分再增加一层，又少21人．一共有几名同学？
<gadget id="calculator">4 + 15 + 21</gadget>
<output>40</output>

<gadget id="calculator">40 / 4</gadget>
<output>10</output>

<gadget id="calculator">2 - 4</gadget>
<output>-2</output>

<gadget id="calculator">10 + 2 + 2 + 2 + (-2)</gadget>
<output>14</output>

<gadget id="calculator">14 * 4 * 4</gadget>
<output>224</output>

<gadget id="calculator">224 + 15</gadget>
<output>239</output>

<result>239</result>