A primary school student takes the same boat to go to an island school. If there are 15 people in each boat, there will be no seats for 3 people. If there are 2 more people in each boat, there will be 5 empty seats. how many boats
某小学学生乘坐相同的船到岛屿学校上课，如果每条船坐15人，则有3人没位置坐，如果每条船多坐2人，则有5个空坐位没人坐，问一共有多少条船．
<gadget id="calculator">3 + 5</gadget>
<output>8</output>

<gadget id="calculator">8 / 2</gadget>
<output>4</output>

<result>4</result>