A bag of melon seeds is 2.5 yuan, a pack of biscuits is 3.4 yuan, a bottle of milk is 2.8 yuan, and a bread is 2.3 yuan. Please put forward one mathematical problem calculated by addition and one calculated by subtraction, and calculate.
一袋瓜子2.5元，一包饼干3.4元，一瓶牛奶2.8元，一个面包2.3元．请你提出用加法计算和用减法计算的数学问题各一个，并计算．
<gadget id="calculator">2.5 - 2.3</gadget>
<output>0.2</output>

<result>0.2</result>