A stationery box is 16.70 yuan, and a box of watercolor pens is 25.80 yuan. Buy a stationery box and a box of watercolor pens with 50 yuan, how much money is left?
一个文具盒16.70元，一盒水彩笔25.80元．用50元买一个文具盒和一盒水彩笔，还剩多少元？
<gadget id="calculator">16.7 + 25.8</gadget>
<output>42.5</output>

<gadget id="calculator">50 - 42.5</gadget>
<output>7.5</output>

<result>7.5</result>