A steel pipe 30 meters long is sawn into three sections. The first section is 7 meters long and 2.5 meters shorter than the second section. How long is the third section?
一根长30米的钢管锯成三段．第一段长7米，比第二段短2.5米，第三段长多少米？
<gadget id="calculator">7 + 2.5</gadget>
<output>9.5</output>

<gadget id="calculator">30 - 7 - 9.5</gadget>
<output>13.5</output>

<result>13.5</result>