The 15 people in the mathematics interest group need to take a group photo. A total of 30 yuan will be paid for sending 5 photos at a time, and 2.5 yuan will be paid for one additional photo.
数学兴趣小组15人要拍集体照，拍一次送5张照片共要付30元，加洗一张要付2.5元，每人一张共要付多少元．
<gadget id="calculator">15 - 5</gadget>
<output>10</output>

<gadget id="calculator">2.5 * 10</gadget>
<output>25</output>

<gadget id="calculator">25 + 30</gadget>
<output>55</output>

<result>55</result>