The school bought 7 boxes of badminton for 91 yuan, and bought a pair of badminton rackets for 28 yuan. How much is a pair of badminton rackets more expensive than a box of badmintons?
学校买7盒羽毛球用去91元，买一副羽毛球拍用去28元，一副羽毛球拍比一盒羽毛球贵多少元？
<gadget id="calculator">91 / 7</gadget>
<output>13</output>

<gadget id="calculator">28 - 13</gadget>
<output>15</output>

<result>15</result>