The school newly purchased 45 footballs, basketballs, and volleyballs, including 15 footballs. The number of basketballs is 1.2 times that of footballs. The rest are volleyballs. How many volleyballs are purchased?
学校新购进足、篮、排球共45个，其中足球15个，篮球个数是足球的1.2倍，其余的是排球，购进排球多少个？
<gadget id="calculator">15 * 1.2</gadget>
<output>18</output>

<gadget id="calculator">45 - 15 - 18</gadget>
<output>12</output>

<result>12</result>