One rope is 3.5 meters long, and the other rope is 2.6 meters long. When the two are connected, the length is 5.7 meters. How many meters is the length of the joint?
一根绳子长3.5米，另一根绳子长2.6米，两根接起来后长是5.7米，接头处长多少米？
<gadget id="calculator">3.5 + 2.6</gadget>
<output>6.1</output>

<gadget id="calculator">6.1 - 5.7</gadget>
<output>0.4</output>

<result>0.4</result>