Naughty bought a water glass for my mother for 2.9 yuan, bought a hat for 3.5 yuan more than a water glass, and bought a pair of gloves. The three items cost exactly 12 yuan. How much is a pair of gloves?
淘气给妈妈买了一个水杯用了2.9元，买了一顶帽子比一个水杯多用了3.5元，又买了一副手套，三样东西正好用了12元钱，一副手套多少钱？
<gadget id="calculator">3.5 + 2.9</gadget>
<output>6.4</output>

<gadget id="calculator">12 - 2.9 - 6.4</gadget>
<output>2.7</output>

<result>2.7</result>