Ding Ding set up a three-layer hollow square array with Go pieces, sharing 120 pieces. How many pieces are there on each side of the innermost layer?
丁丁用围棋子摆了一个三层的空心方阵，共用了120个棋子，问最里边一层每边有多少个棋子？
<gadget id="calculator">120 / 4 / 3</gadget>
<output>10</output>

<gadget id="calculator">10 + 3</gadget>
<output>13</output>

<gadget id="calculator">13 - 4</gadget>
<output>9</output>

<result>9</result>