15 students took a group photo, and each person asked for a photo. The first three photos and one negative cost a total of 2.70 yuan, and a photo was printed later at 0.40 yuan. How much does each person pay on average.
15个同学合影留念，每人要一张照片，最初三张照片和一张底片共收成本费2.70元，以后加印一张照片收费0.40元．平均每人应付多少元．
<gadget id="calculator">15 - 3</gadget>
<output>12</output>

<gadget id="calculator">12 * 0.4</gadget>
<output>4.8</output>

<gadget id="calculator">4.8 + 2.7</gadget>
<output>7.5</output>

<gadget id="calculator">7.5 / 15</gadget>
<output>0.5</output>

<result>0.5</result>