Li Hong has 10 yuan. He bought a ballpoint pen for 2.85 yuan and a triangular board for 1.65 yuan. How much should he get back?
李虹有10元钱，他买了一支圆珠笔2.85元，一则三角板1.65元，应找回多少元．
<gadget id="calculator">2.85 + 1.65</gadget>
<output>4.5</output>

<gadget id="calculator">10 - 4.5</gadget>
<output>5.5</output>

<result>5.5</result>