10 students take a group photo, according to the regulations, it costs 12.5 yuan to develop 4 photos. Since each of them asked for a photo, they shared 21.5 yuan. How much does it cost to add a photo?
10位同学照合影，按规定冲洗4张照片共需要12.5元．由于他们每人要了1张照片，共用了21.5元．加洗1张照片需要多少元？
<gadget id="calculator">21.5 - 12.5</gadget>
<output>9</output>

<gadget id="calculator">10 - 4</gadget>
<output>6</output>

<gadget id="calculator">9 / 6</gadget>
<output>3/2 = around 1.5</output>

<result>3/2 = around 1.5</result>