There are two identical colored ribbons, red and yellow, each with a length of 13.5 decimeters. The red ribbon uses 7.8 decimeters, and the yellow ribbon uses 6.9 decimeters. Which ribbon is the longest? How many decimeters long?
有红、黄两根同样的彩带，各长13.5分米，红色彩带用去7.8分米，黄色彩带用去6.9分米，哪根彩带剩下的部分长？长多少分米？
<gadget id="calculator">13.5 - 6.9</gadget>
<output>6.6</output>

<gadget id="calculator">13.5 - 7.8</gadget>
<output>5.7</output>

<gadget id="calculator">6.6 - 5.7</gadget>
<output>0.9</output>

<result>0.9</result>