junior high school student took a minibus to visit the Science and Technology Museum. If there are 15 people in each car, and there are 9 people left, if there are 18 people in each car, and there is just one car left, how many minibuses were originally planned to be used?
某校初一学生乘中巴车去科技馆参观．如果每车坐15人，还剩9人，如果每车坐18人，刚好剩余一辆车，则原计划用几辆中巴车？
<gadget id="calculator">18 * 1</gadget>
<output>18</output>

<gadget id="calculator">18 + 9</gadget>
<output>27</output>

<gadget id="calculator">18 - 15</gadget>
<output>3</output>

<gadget id="calculator">27 / 3</gadget>
<output>9</output>

<result>9</result>