There are 5 numbers in a row, the number in the middle is the largest, counting forward from the middle number, one number is 3 less than the other number, and counting backwards from the middle number, one number is 4 less than the other number, the 5 numbers The sum is 69. So what is the number in the middle?
有5个数排成一列，中间一个数最大，从中间的数往前数，一个数比一个数少3，从中间的数往后数，一个数比一个数少4，这5个数的总和是69．那么中间的数是多少．
<gadget id="calculator">3 + 6</gadget>
<output>9</output>

<gadget id="calculator">4 + 8</gadget>
<output>12</output>

<gadget id="calculator">9 + 12</gadget>
<output>21</output>

<gadget id="calculator">69 + 21</gadget>
<output>90</output>

<gadget id="calculator">90 / 5</gadget>
<output>18</output>

<result>18</result>