Students A, B, and C jointly bought 17 commemorative cards, but C did not bring any money, so A and B paid for 6 and 11 commemorative cards respectively. It is known that B and C bought 2 less than A, and C returns B 1.25 yuan, how much should A return to B.
甲、乙、丙三个学生合买17张纪念卡，丙没有带钱，由甲和乙分别付了6张和11张纪念卡的钱．已知乙、丙比甲少买了2张，丙还给乙1.25元，甲应该还给乙多少元．
<gadget id="calculator">17 - 2</gadget>
<output>15</output>

<gadget id="calculator">15 / 3</gadget>
<output>5</output>

<gadget id="calculator">1.25 / 5</gadget>
<output>0.25</output>

<gadget id="calculator">2 * 2</gadget>
<output>4</output>

<gadget id="calculator">17 + 4</gadget>
<output>21</output>

<gadget id="calculator">21 / 3</gadget>
<output>7</output>

<gadget id="calculator">7 - 6</gadget>
<output>1</output>

<gadget id="calculator">0.25 * 1</gadget>
<output>0.25</output>

<result>0.25</result>