The first graders of a certain school held a spring outing. If they rented a 45-seater bus, 15 of them would have no seats; if they rented the same number of 60-seater buses, one bus would be empty. How many first graders are there in this school?
某校初一学生举行春游，若租用45座客车，则有15人没有座位；若租用同样数目的60座客车，则有一辆客车空车．这个学校初一学生有多少人？
<gadget id="calculator">60 + 15</gadget>
<output>75</output>

<gadget id="calculator">60 - 45</gadget>
<output>15</output>

<gadget id="calculator">75 / 15</gadget>
<output>5</output>

<gadget id="calculator">45 * 5</gadget>
<output>225</output>

<gadget id="calculator">225 + 15</gadget>
<output>240</output>

<result>240</result>