7 students took a group photo, and the price was 12.5 yuan according to the regulations to wash 4 photos. Since each of them wanted a photo, they shared 17 yuan. How much does it cost to develop a photo?
7位同学照合影，按规定定价12.5元洗4张照片，由于他们每个人要一张照片，共用了17元．加洗一张照片需要多少元？
<gadget id="calculator">17 - 12.5</gadget>
<output>4.5</output>

<gadget id="calculator">7 - 4</gadget>
<output>3</output>

<gadget id="calculator">4.5 / 3</gadget>
<output>1.5</output>

<result>1.5</result>